External monitor image distortion

Try booting once in safe mode (https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac). Beside disk check, minimal extensions load and other things there also the deletion of various cache files and sometimes gives good results.

Personally I would reset both the Mac's nvram (https://support.apple.com/en-us/HT204063) and the LG display to factory settings.

Have you tried switching the HDMI port from 1 to 2 (or viceversa) if the display has two if them?

Hi arendfromburbank,

Thanks for reaching out using Apple Support Communities. Here to help.

We understand you're having trouble with the connection of your MacBook Pro to an LG monitor.

You mentioned using an adapter or USB hub for this connection. Are you referring to the Apple USB-C Digital AV Multiport Adapter? If using an adapter other than this one, we aren't able to verify compatibility or performance for various scenarios. You may want to consider contacting the vendor of your USB-C Hub, or consider trying the Apple USB-C Digital AV Multiport Adapter. More about this adapter can be found below.

Apple USB-C Digital AV Multiport Adapter

Hope this helps! If we can assist any further, just let us know!