I'll build off of what Noodles' mum said (she's 100% spot on about prolapse if your bird forces too much or intestinal problems if your bird holds it too much).
For potty training, you should be doing roughly what was described above. It's called capturing (see a link here about it
https ://www.exoticdirect.co.uk/news/how-train-bird-using-positive-reinforcement). It's really parrot-initiated training where you build positively off of their actions. Example: if your bird shakes before going poo, then you quickly shift them to their poop perch and praise when they go poo there. It was also going to happen (they needed to relieve themselves), you just built off of it and made it a success.
We have 2 set places for pooping in the house - his cage door and his training perch (both are in different rooms) - and our little guy is fully-flighted, so he'll just fly there.
Now, like any training, YOU the human have to be consistent. What worked for us was spending one weekend when we had the time to keep a close eye on him. The moment he gave his body shake or his poop squat, we swoop him up and put him on his poop perch, then gave our cue word as he went, then praised and treated. He learned within a day.
When we go on walks outside, his body cues are always listened to, but in addition to that, if he doesn't give a cue but it's been about 15 minutes, we'll put him on a perch and tell him the cue word. At that point he'll either go or he won't - we don't force him either way. If he doesn't go, we just continue on our way. If he does, then treat if you're still at the beginning stages of potty training so he solidifies that association.
But just because they learn within a day doesn't mean YOU the human can slack off. If you are inconsistent, the training can easily be undone.
Nowadays, our main problem is revenge poops - when he's upset at us, he'll purposefully fly to the wrong place, make eye contact, and go.