I just wanted to add my experience here.
I have autistic DC. My DS who is now 14 years old is still incontinent, both day and night. But for a while when he was young, the continence team worked with him to try and solve his problems.
His twin sister is also autistic, and she wasn't quite dry through the night at age 4.
We were referred to the continence team when they were both 4. Primarily for DS, but because DD wasn't dry either, they included her in the referral.
I had to fight tooth and nail with the continence nurse NOT to treat DD. They wanted her to take a medication that would physically stop her being able to urinate during the night. The nurse warned me that it was a powerful drug and that it was imperative that DD didn't drink a single thing after being given the medication, not even a sip of water.
Honestly, there was no way that I was going to give my 4 yr old such powerful drugs for a problem that she would probably just grow out of. (And she did, around six months or so later, she was dry.)
Nothing was suggested for DS as he didn't just pee throughout the night, he also defacated (and still does). So there wasn't any meds suitable or else they probably would have suggested those too!
So I just wanted to say that sometimes they do treat children at a surprisingly young age, but imo, treatment isn't always the best option. I remain quite shocked to this day that such a powerful drug was being suggested to medicate a very young child unnecessarily.
As an aside OP, mattress protectors really do work - my 14 yr old regularly has accidents of both pee and poo throughout the night. Have you tried the age-old suggestion of doubling up? So if there's a wet night, you just need to whip off the top sheet and protector, and you're left with a fresh sheet and mattress protector underneath?