Can't delete photos from my LG X Power
Using SD Maid - system cleaning tool (free version) to clean the device and delete those files using built-in file explorer solved the problem for OP. From app description

Nobody is perfect and neither is Android.
Apps you have already removed leave something behind.
Logs, crash reports and other files you don't really want are constantly being created.
Your storage is collecting files and directories you don't recognize.

That said, I have no clue of what exactly caused the problem and why other apps couldn't delete the files. Or how this app fixed the underlying issue.
I am not affiliated with the app. I've been happily using the pro version for years with scheduled operations to keep the device clean.