Potty training going backwards...

Hello dear mamas,
I'm trying to get my son potty trained and I would love to get your advices.
He's almost 2 1/2 and so far he did good. I even thought to myself that it will be easier than expected. How naive.. But lately it hasn't been doing too good.
I'm trying since he's 2 more or less but I take it easy and do not want to push him at all. I live in Portugal and during all summer he was basically naked to whole time and he learned quite quick to do it in the potty. But as soon as he wears anything, undies, short etc, he thinks it's a diaper. I tried few days to still put him shorts to teach him to pull them down. But he didn't mind being dirty at all. Lately, I tried to put him on the toilet in the morning and evening but it's going in the opposite direction. He now decided to pee anywhere, asks to wear diapers, refuses to sit on the toilet etc. When he uses the potty, it's now an exception.
So as I already mentioned, I don't want to pressure him and if it's going to take much longer, so be it. But I was wondering if some of you went through this as well or has any suggestions on how to proceed softly? Autumn is slowly coming and I would somehow love not having to wash 10 000 pairs of pants per day ;)
I guess wait and keep trying?
Thank you all for your answers!