LRC running slow after update

Please post your System Information as Lightroom Classic (LrC) reports it. In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut out as that is just so much dead space to us non-Techs and it takes up vast amounts of scroll space making the reply less readable and less likely that others will bother with your post. Also large amounts of text in a post also render the Translate function inoperable...

You didn't provide any detail about your computer.  Without that, it is only guessing.  You might try letting it stay open on your computer overnight.  It could be finishing the update in the background.   You can also look here for suggestions:  https://helpx.adobe.com/lightroom-classic/kb/optimize-performance-lightroom.html