What AMD Radeon graphics card are you having issues with?
I have had major issues with kmod-515-drm driver after upgrading to FreeBSD 14.0 (worked fine with 13.x).
There is a known issue with the kmod-515-drm driver with certain Radeon cards such as the 6750XT and 5500XT (like mine) where the driver would cause hardware resets due to various conditions (
https://github.com/freebsd/drm-kmod/issues/263). Down grading to kmod-510-drm (compiling from ports) or later upgrading to kmod-61-drm driver (again compiling from ports) did resolve the issues for me.
Please try compiling from ports either the kmod-510-drm or kmod-61-drm driver from ports. You will need the FreeBSD 14.x (/usr/src) sources as well as the ports tree (/usr/ports), checkout the FreeBSD handbook on freebsd.org website (it is quite helpful!).
1. Pull the sources for FreeBSD (FreeBSD chapter 26.6) and the ports tree (FreeBSD chapter 4.5) via Git (can install Git using pkg).
2. Use pkg to uninstall the existing drivers - do not reboot.
3. Compile the kmod-510-drm (usr/ports/graphics/drm-510-kmod) or kmod-61-drm (/usr/ports/graphics/drm-61-kmod) driver by using 'make install' inside the directory for the choosen driver (needs to be compilied using root or sudo).
4. Reboot (no need to change the rc.conf, the various drivers use the same config).
Try that, hopefully it will resolve your issues.