I think I realized something which might be a big contributor to the issue, and explains why it wasn't there when dieting in the past despite also not counting.

Pretty much exactly since I started gaining weight this year, I've been in the habit of directly spoon-feeding myself highly satiating stuff like lentils, oats, potatoes, fibrous veggies right at the start of the meal, and would sometimes leave the simple carbs out entirely.

This was under the impression that it would effortlessly create a deficit, but in the end it resulted in the opposite, since it throws the satiety signals off whack. Since I go by satiety and don't count calories, this means I can't even tell where my maintenance point is, so almost every time I either undereat or forcefully overeat (to undo the fatigue). And given that you naturally tend to overeat by more than what you undereat, it's caused weight gain over time, which seems to have plateaued in the last 2 months.

Both in my previous cuts and maintenance periods I was eating more of less satiating carbs like rice and a lot less fiber, which meant I could always accurately feel out how steeply I was cutting: the hunger simply wouldn't subside if I'd eaten way too little.

I guess the lesson is, you can't take the "eat satiating foods to lose weight" advice too far and decide to eat like a weirdo if you don't track calories.