TLDR: Sounds about right to have a gap with belt v beltless. For powerlifting purposes then it doesn’t really matter. You can choose to improve your beltless performance if you wish. For sports/athletic performance there’s other considerations.
Squatting more with a belt than without is pretty common and in people who have more than a few weeks in a belt pretty much a given.
The difference between the numbers comes down to several factors e.g. training history including how much beltless work has been or is done by an athlete.
I dunno what you were expecting exactly when you loaded up 75% of your belted max.
No surprises that it was a harder or higher RPE cos 75% 1RM with belt is something > 80% 1RM beltless. Most of the time I’ve seen belted and beltless treated as two different movements/exercises each with their own max off which to program.
As if whether or not this is worth working on…This is in the powerlifting section so the goal is to up the comp movements and nobody cares for how much you can squat beltless or how close to your belted squat it is. That’s not to say there shouldn’t be any beltless work at all or minimal beltless work. There’s an arguments from both extremes and plenty who advocate for a middle ground but that’s something for another thread.
If there’s some goals involving improved performance in sport where you won’t be wearing a belt then maybe it’s worth working on but that’s another story also.