This was a problem in earlier beta 4.5 which has been recently fixed.
I think the busy cursor also occurred in 4.4 for some users, not sure if it was
Linux, but that is very likely.
Can you update your
OpenCPN to the the beta version, or at least install it concurrently and try it to see if it fixes the problem? 4.5 has improved significantly and I think it is quite stable.
Perhaps another Linux user has some suggestions for you.