I've been using LrC on my PC for many years without serious problems but actually it freezes when using the "copy develop settings" option (Ctrl+Shift+C). No reaction to any further mouse clicks, menues are all grey. The only possibility to go ahead is "Esc" but then the develop settings are not copied and cannot be pasted to other photos.
LrC Version 12.1
Windows 10, latest version.
Try resetting your Lightroom preferences:
https://helpx.adobe.com/lightroom-classic/help/setting-preferences-lightroom.html
Also see: https://community.adobe.com/t5/lightroom-classic-discussions/important-steps-for-manually-resetting-preferences-omitted-from-help-article/td-p/12972518
Quit Lightroom Classic.
macOS: Press and hold the Shift + Option keys.
Windows: Press and hold the Shift + Alt keys.
While holding down the keys, launch Lightroom Classic.
When asked, select "Yes".
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