Can a latch be used instead of a handle on the front door?

Hello,
I have a little house and go in and out a lot,
for example also because I have an outdoor toilet.
Until now, my front door has a fixed knob on the outside, which cannot be opened,
so I always keep the key in it.
I often have guests and twice it has already happened that they locked themselves out.
May I install a handle on the outside of my front door instead of a fixed knob, or would the insurance then no longer pay in the event of a break-in?

I'll put it this way... leaving the key outside can't be worse for the insurance. Just ask them—preferably always get it in writing in the [VSchein]... GD

Am I allowed to install a lever handle instead of a fixed knob on the outside of my front door, or would the insurance then not pay out in case of a break-in?

You are allowed to do anything. However, in the event of a break-in and an unlocked door, you must be aware that the insurance will at least claim gross negligence.
Apart from that, I find it terrible always having to lock my front door from the inside so that no one can get in (with a lever handle, you visually invite everyone to just walk in). Better no lever handle and use a latch instead. It's less conspicuous.

Until now, my front door has a fixed knob on the outside, which cannot be used to open it,

... in that case, the inconspicuous conversion to a rotating knob would seem more obvious to me than to a lever handle.

Thank you for your answers!
Best regards!

We already had handles on both doors in the old house and have them on the outside of both doors in the new house as well. It would really annoy us if we always had to take a key with us when we go out. I would regularly lock myself out because I would forget it. I also don’t know why I should lock my door from the inside when I am at home. Windows and patio doors are also left open if the weather is reasonably good.