I think this is really a job for tech support, but I can't seem to find the "pros" who chat all day. I've been using LR for years, but I don't like the $9.99 monthly rental and seemingly non-existent personal support.
If you think it has switched libraries (not sure why you think that), try File->Open Recent
My thought is that your monitor has a corrupted profile, see How do I change my monitor profile to check whether it’s corrupted? - The Lightroom Queen
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