Wayland seems ready to me but the main problem that many programs are not configured / compiled to support it. Why is that? I know it's not easy as "Wayland support? Yes" (but in many cases adding a flag is enough but maybe it's not a perfect support). What am I missing? Even Blender says if it fails to use Wayland it will use X11.
When Wayland is detected, it is the preferred system, otherwise X11 will be used
If an app has only ever supported X11, then it probably doesn't care about those limitations (the apps that do care probably already have a Wayland version). And if an app doesn't care about the extra stuff Wayland has to offer, then there's not really a reason to add the extra support burden of Wayland. As long as they work fine in XWayland, I think a lot of apps won't switch over until X11 support starts dropping from their toolkit, and they'll just go straight to Wayland-only.
Plasma deprecated their X11 session in v6 pending removal in the future, and Redhat has already dropped it in Fedora & will do for EL in the next release.
Plasma didn't deprecate X11. Though some developers hinted that the Xorg session will probably be dropped before Plasma 7 and before Qt drops X11. But nothing concrete.
Oh indeed not deprecated, my bad. Wayland is default and "preferred" (how they're deciding what to prefer I can't imagine), and X11 is confirmed to be removed in a future release.
X11 has exactly one developer who's a vaccine denying turbocunt German, everyone else has dropped it and it's codebase is practically unknown territory with security risks.