Which furniture stores can you recommend?

Thank you for your help

here are two pictures showing what we are roughly looking for
We are simply looking for modern timeless furniture that is white with wood accents

Is there perhaps an online shop or a furniture store with an online shop that brings together all well-known and relevant furniture brands?

then we can look there to see which furniture we like
we want to have all the furniture for the living room and dining area, for example, from the same product and design series so that it is consistent

here are two pictures of what we are roughly looking for

With furniture like this, you are flooded in furniture stores in all price and thus quality categories (mainstream). We once had Hülsta Xelo, fits your pattern.

Thank you for the example pictures, your requirement is now very clear.

we want the living room and dining area, for example, all furniture from the same product and design line so that it is uniform

Only Knuffmann in Neuss and Sijben in Roermond remain from my recommendations. The other stores I mentioned are too individual and do not have uniform living room furniture from one manufacturer on display, and the value of a consultation for a composition is not high for you. You can basically go to any furniture store that arranges the furniture in "rooms."
With these requirements, some manufacturers are ruled out, as not every manufacturer builds complete design lines as you wish. I would start with Hülsta and Musterring and if the price gets tight, ask on-site what is offered one class below each.

Is there perhaps an online shop or a furniture store with an online shop that unites all well-known and relevant furniture brands together?

Online you will not get a quality impression.

I wanted to have an online shop where all relevant manufacturers are available.

Then we can see which manufacturers are interesting and then specifically look for these products in furniture stores and get an impression of the quality.

Then we have a large selection for all pieces of furniture and can finally choose a handful and then look at them on site.

Also take a look at furniture from Hartmann, such as the [Caya] and [Vara] series. Top quality, they are produced here on a large scale. Available in many large furniture stores but also directly from the manufacturer in Beelen near Münster or in their online shop.

We are simply looking

SIMPLE is a general word for difficult to you? As and many others have already said: go to furniture stores, look around, try out and choose. You will notice the quality yourself. I have to be honest: I would have already checked all the stores if I were you or your wife... You can't choose furniture in a forum ;)