gbm_bo_get_fd_for_plane isn’t exposed by libnvgbm.so.
It was added to the Mesa GBM implementation in: gbm: add gbm_bo_get_fd_for_plane (!5442) · Merge requests · Mesa / mesa · GitLab
Despite libnvgbm.so being seemingly based on minigbm, its source code doesn’t seem to be available in the L4T source package.
(This is a requirement for recent Xwayland)
Update: I switched to using GitHub - OE4T/tegra-udrm-gbm: Wrapper for libnvgbm.so to work with Mesa's libgbm backend loader instead, which allowed for upstream Weston to load.
Note however that something on the system seems to be overriding libgbm.so.1 to libnvgbm.so on each package install, which is really annoying. Any idea of which postinst script does that, so that I can turn that behaviour offline permanently?
For information, do you use Jetpack 4.6.1 or 5.0 DP?