I upgraded my test laptop to 12.1 and I confirm the problem I've seen already configuring Jenkins builds on 11.3. Probably the problem is not related to FreeBSD upgrade itself, but to upgrade of some packages.
With the default configuration meson cannot find x11 and x11-xcb libs.
To build EFL I need to patch src/lib/ecore_x/meson.build replacing:
x11 = cc.find_library('x11', required: true)
x11 = cc.find_library('X11', required: true)
x11_xcb = cc.find_library('x11-xcb', required: true)
x11_xcb = cc.find_library('X11-xcb', required: true)
Yes, it is the problem of CAPITAL.
Indeed, the library is named as libX11.so, not libx11.so.
Probably, something should be adjusted in meson build files.