I was wondering if if would be possible to network boot CM4s from a TFTP Service just line one would be able to also do with a common PI. Will that be possible?

Yes i think that should work. Other pi’s can do that.

Well, that way I would not need any PI with flash but could NetBoot and I am done 🙂

Yes idd. My setup has 3 pi and a tx2 nx. The tx2 is going to provide the NetBoot functionality and the K3s

@__rxb__ I have a similar setup in mind with the one slot providing everything from the SSD

More info on how to do that here: https://www.raspberrypi.com/documentation/computers/remote-access.html#network-boot-your-raspberry-pi

I did this a couple of times already with pi3&4 but never with a CM.

I got a bunch of CM4 booting through https. Quite well documented and easy to implement, as is the TFTP boot.