4 year old refuses the potty/toilet - end of my tether!!

Hey all, stay at home dad here with a 4 year old lad. Been attempting toilet training since he was about 2.5. We started a little late due to some health dramas in the family and I also missed the signs when he first was interested in the toilet at about 2 ish (oops!!). I'd start then give it a break to reset and we've done this a number of times now.

HE's done literally everything he needs too - He's dry all night. He tells me he heeds a wee or a poo. He's in undies all day but he just REFUSES the potty or toilet (with adapter) and will only go in nappies still.

When he needs to go he just goes and gets one, or requests one.

I'm out of ideas, I've tried bribes (got 3 drops of wee in a potty then nothing as he got his reward lol). I've tried kindness, frustration the works.

Has anyone had this and if so what did you do. I wanted to not provide nappysd anymore but then i got worrid he's hold everything in and give himself issues down the line.

thanks!!! HELP