I had something like this in an LCD that got moisture in it, it also might been due to mechanical damage (pressing on these spots too hard, so the diffusion layers got mangled). It's an issue with the internal diffusion layers of the LCD screen and unfortunately I don't think there is an easy fix for that, even if you disassemble the panel and manually clean the diffusers, it probably would be impossible to realign them correctly, and also a lot of dust could get inside in the process. I don't think this is a problem with the "liquid-crystal" part of the LCD.

lighter ones can be moisture and cleaning them is possible https://www.eevblog.com/forum/repair/computer … monitor-blotch/
darker ones is damage, either mechanical or heat/age related and permanent