For GTK 4, we should make sure that certain dependencies are required from the start. Most importantly, we should require libwpe and wpebackend-fdo to ensure nobody is still using -DUSE_WPE_RENDERER=OFF.
I think we should also require libepoxy, and also libsoup 3 (if that's not required already).
Yes, the idea is to make all deps that are optional because of the deps policy mandatory for gtk4 build (soup3 and wpe for sure)
Other libs we could possibly require: libmanette (doesn't exist in RHEL, but probably should), libsecret, enchant, libhyphen, libtasn1, openjpeg, woff2, lcms2
Stuff we probably (?) don't want to require: jpegxl (experimental), libnotify (deprecated and bad), libgcrypt (bad, could be replaced with OpenSSL WebCrypto backend), avif (experimental), thunder