Hi there, welcome!
Disclaimer: A non-Nvidia user here... 
Could this (open) issue be the same as yours?
https://github.com/Askannz/optimus-manager/issues/464
In general, I learned in the past that it is kind of suggested the use of prime rather than optimus-manager (although I see there are several users in the forum adopting it).
See e.g. this thread (but there are several others similar).
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