Signed up here just to confirm this also just resolved the same issue for me. Not sure why Parallels can't resolve this with an update, probably because it doesn't make financial sense to them but quite annoying that a software just stops working and you have to debug it to find a post from a user with the solution versus the company actually being proactive about it after it was reported with a solution.
Hello, Parallels Desktop 12 is not compatible with Mac OS Big Sur 11.2.3. Please refer to this KB article to know the compatibility between the Mac OS and Parallels Desktop.
Hello, please provide us with the screenshots of the error message, so that we can resolve the issue. Thanks.