This was pretty much the information I got.
When my son was young we did try toilet training and it just caused withholding issues both urinary and bowel withholding.
Then we got told to wait for signs of readiness by our HV, this was during covid when HVs couldn't come to your home. They did a basic questionnaire about milestones, which he was missing quite a lot of and the HV said don't worry most children she's encountered are missing a lot of these milestones because of isolation, but to keep doing that we're doing and he'll catch up.
Then when he started nursery we were told what are you on about don't wait for signs of readiness. My head was spinning. So we tried again and his withholding issues got worse.
When he started school aged 4 the school referred us to their HV who was so lovely and she'd come to our house. By this point we had received an autism diagnosis already. The HV would observe us and the issues we were having and she finally said she hasn't got anymore ideas and referred us to ERIC for a webinar specifically for SEN children.
The webinar couldn't have been more confusing or contradictory.
Don't wait for signs of readiness, go to a schedule and build a routine... except if your child shows signs of anxiety and then a routine can just cause apprehension. Always change your child in the bathroom without exception so they can learn the bathroom is where we do our business... except if bathrooms are sensory nightmares for your child and cause distress. Completely get rid of nappies and move over to pants... except if your child withholds and then always make sure they have access to nappies or pull ups. Always give lots of praise to your child as they respond better with rewards... unless your child is demand avoidant or hates being perceived like many autistic children and then never reward them because it highlights they're doing something and they will probably stop doing it. Always go straight to a toilet and never use a potty because transitions can be stressful... unless they need a potty because the transition to the bathroom can be stressful.
Like the information we were given was all sort of common sense things. I'm sure it benefitted some people, but I know many, like me, have already observed these struggles in their children and have already come to these conclusions themselves which is why we were desperately watching for advice.
Half the webinar was spent plugging their own products but not actually explaining why they were helpful.
Eta: oh the other one they advised. Always put the poo from the nappy into the toilet and let your child watch.
Well all this did for us was encourage smearing. My child who never smeared before started taking the poo out of his nappy because he realised it was something he could move about instead.