Any new fit or replacement will mean a Mode S
Correct, and strongly to remember for everybody in the EU: the possibility for 1:1 replacement of old and/or defective avionics expired last year in November.
So, if something breaks, such as an old Mode-C/A XPDR, you are no longer allowed to stick in another old Mode-C/A, you have to comply with new rules = if your Mode-C breaks, you have to put in Mode-S, same is true for COM: if your venerable COM breaks, you have to put in 833 COM. Many are not aware of that.