I am experiencing the exact same problem.  It started a couple of weeks ago after an update.  My company files are 137,000kb and 57,000kb.  I have restarted my computer multiple times.  I have tried manual updates but I am fully up to date.  The only way I could find today to switch companies was to close QB, then double-click on the .QBW file in my C drive folder.  The company opened, and then I was able to switch to the other company as it has always done for the last 25 years.  I am using QB Desktop Pro Plus 2023.