DIAGNOSIS: That's called "DSE" or Dirty Screen Effect. It's not actual dirt; it's an artifact of the mini-LED backlight array and the diffuser layers not being perfectly uniform, causing faint cloud-like patches, especially noticeable in solid color or panning shots.
FIX: Unfortunately, DSE is a panel lottery issue inherent to the manufacturing process, not something you can clean or adjust away. You can try a panel uniformity test via the built-in YouTube app (search for "DSE test" videos) to see how severe it is. If it's minor, most people's brains tune it out after a while during normal content.
IF THAT DIDN'T WORK: If the patches are severe, blotchy, and distracting during regular viewing, and the TV is within the return window from your retailer, that's your best recourse. If it's under manufacturer warranty, you can contact TCL, but they typically only authorize a repair/replacement for very extreme, obvious uniformity failures.
HEADS UP: Don't press on the screen trying to "massage" the spots out—you'll damage the delicate mini-LED array and void your warranty. It's an internal optical issue, not a pressure thing.