LAN / WLAN / Telephone - looking for suitable hardware components

The picture is correct.

A somewhat "more modern" approach would be the use of IP phones. They connect to a normal (orange in the picture) LAN port or even via WLAN. Either at the switch or directly at the router, that doesn’t matter. Strictly speaking, you can connect them to a port anywhere in the world...

The advantage is greater flexibility. I can move my DECT stations (if I notice there is no reception in the garden anymore, I go closer to it), I can relocate my office to the former children's room, I can make calls via my mobile phone (app), assign multiple numbers from virtual providers to the phones, and possibly save myself the adapter stuff (and the purple part of the picture).

The only challenge can sometimes be obtaining the access data (so-called SIP credentials) from your provider. That can take a while, so you should clarify it in advance.

Ah – and of course it requires IP-capable phones/base stations. The old base stations have to be replaced. The old handsets usually still work (with DECT).

Yes, something like that is still not 100% accurate but comes very close to what you ultimately want.

And what is still inaccurate?

Ok, WLAN switches don’t exist, they are actually called WLAN access points and practically do the same as a switch, just without cables, and can, as is common nowadays, additionally bridge between LAN and WLAN.
If you have multiple WLAN access points in the house, they should be from the same manufacturer and operated in an "Extended Service Set" so that a single large WLAN network is created in the house.

Something "more modern" would be the use of IP phones, though. They connect to a regular (orange in the picture) LAN port or even via Wi-Fi. Either on the switch or directly on the router, it doesn’t matter. Strictly speaking, you can plug them into a port anywhere in the world...

And do I not have to pay attention to anything tariff-related with the provider? So classic DSL + landline works with it? That means I only need to get the special digital access data from the provider? Or can I then save the "+ landline" (but I still need a phone number, right)?

And do I not have to pay attention to anything tariff-related with the provider? In other words, does classic DSL + landline work with it? So I only need to get the special digital access data from the provider? Or can I then save the "+ landline" (but I still need a phone number)?

Clear maybe.

Classic landline hardly exists anymore. New contracts are only for business customers anyway, old contracts are gradually being converted. That means everything is already VoIP. (Voice over IP, internet telephony) And if that is the case, the access data is also provided. Since last year, providers are also obligated to release this data. For some, it is included directly in the contract, for others only after multiple requests...

Exceptions are some cable contracts. They sometimes use a different telephony system than VoIP. In that case, you may have to book additional telephone services to get VoIP.

Regarding the "+ landline": there are also online providers that offer (partially) free phone numbers. Only the number, of course, not the telephony. So I might be able to save the telephony service from the internet provider if they offer that. I can then use these numbers with any IP phone and plug it into any LAN socket in the world (as long as it has internet) and always have my "landline" with me. Or, as mentioned, my mobile is on Wi-Fi and an app handles the landline telephony. Also very cool.

And what else is inaccurate?

This is how the image is correct:

Ok, WLAN switches do not exist, they are actually called WLAN Access Points and practically do the same as a switch but without cables and, as is common nowadays, can additionally bridge between LAN and WLAN.

Yes, exactly, WLAN switches do not exist... they are called Wireless Access Points and that's how we want to call them; anything else just confuses the next person...

A hub and a switch practically do the same, but there is still a difference...

You understood it. The functions will not be disturbed by you using some words incorrectly from a technical point of view.

So I only respond to your questions out of politeness now, since the clarification goal "understanding" is actually already achieved.

First TAE.
The first TAE in the signal path is the one where the responsibility is handed over from the connection provider to the person who then lays the further cables inside the house. It is also called monopoly TAE.

Router.
That is an IT thing, a kind of control center for data signals. Inside the housing of a "Fritzbox / Homebox / Easybox / Digitalization box" there is such a thing. That the same device also has sockets for telephones does not mean that telephone signals also belong to the router’s business. These hybrids of router and mini telephone system do that in another "heart chamber".

Plugging in ports.
Of course, you only need to bring to the patch panel those connections of your Dunennstihn router that you actually want to use. The patch panel is just an "extension cable" towards all sockets. Connections on the Dunennstihn router intended for analog telephones often have RJ11 sockets. Yes, then you have to translate them to the wider Western siblings, since patch panels everywhere start from RJ45.

LAN.
The patch panel connects passively, without any intelligence, the plugged connections 1:1 with each other. The neighbors do not "see" each other among themselves, all connections are exclusively "tunneled" separately through their cables. They just lie on the same "board". The LAN (in the sense of the IT network) can also use this cable house network. The cable house network / you call it LAN but it is not identical to what the computer people call LAN. The LAN you call (with analog telephones) and the LAN (the IT one) exist separately and peacefully side by side.

Any branch line from a cable branch to a socket can change its type at any time – simply by plugging an IT connection there instead of a telephone connection. Therefore, all sockets of such "structured cabling" have all usage possibilities – simply by the simple trick of connecting every cable with all its wires at its socket. In this "sum" of wires, both those needed by the telephone and all those needed by IT are contained. That is the whole magic. The patch panel itself is passive, it only "routes" by connecting the cables.

Note well: your understanding of the content is not disturbed by the terminology confusion. It can only irritate readers who are following along.

The only challenge can sometimes be to find out the access data (so-called SIP credentials) from your provider.

You need SIP accounts when you want to use Voice over IP on the public network (= on the line between the provider and the external side of the Erheißtnich router) (which is common nowadays, since ISDN lines are being switched off). Already before the switch (or independently of it), you can connect IP phones to your Erheißtnich router. This "internal" connection of these devices does not need access data. Therefore, plugging from the guest room to the living room does not depend on knowing the "valid registration data".