@cblgh Did more testing, it's looking for libwebkit2gtk-4.0.so.37, Guix has libwebkitgtk-6.0.so.4.0.3 and libwebkit2gtk-4.1.so.0.8.3, and some symlinked variants with simpler names, but no libwebkit2gtk-4.0. So all the webkitgtk libraries are newer.
Most generically named one is libwebkit2gtk-4.1.so.
@cblgh That means an FHS container won't be enough, I'd have to fake the library names somehow. This might manifest on other distros too that have different (mostly newer) versions of WebkitGTK.