Let me guess, you only have 8G GPU mem ?
If you search posts on this forum, you will see many gamers having problems with this error, mostly with older cards with only 8G GPU mem. Those with AMD GPUs have found that rolling back GPU drivers can fix the problem. Old Nvidia Cards, we are still not sure how to fix it ? I use to own a 1080 and continually got this error message, so upgreyyed my GPU.
I suspect it has to do with old shader caches ? You need to delete all the possible locations, then redownload and reverify
(1) Steam / Bannerlord
(2) "C:\ProgramData\Mount and Blade II Bannerlord"
(3) "NVidia also keeps a shader cache located in %LOCALAPPDATA%\NVIDIA\DXCache and %LOCALAPPDATA%\NVIDIA\GLCache ..".
Also look at the Cloud, could be another copy there, somewhere ???