It's not jumping to a life changing conclusion to look at parenting strategies suggested for ADHD, read up about it if you want to and/or to keep it in the back of your mind for later. It's also not jumping to a life changing conclusion to ask the GP or health visitor what they think about his behaviour currently and whether it merits an assessment - it is highly likely, that as you say, they will say "No problems at nursery? Don't worry then, wait and see how he does at school and come back if you have any concerns." But the note that you presented with concerns at age 4 will be there later if you need it, and won't change anything at all if you don't. They might also offer you access to a parenting class, which probably won't teach you anything groundbreaking, but may be useful in that children who have more challenging behaviour can often need a more structured approach and the way that you implement all the usual stuff like rewards, praise, consequences, reminders, encouragement etc matters more. So while 90% of parents can get away with doing it this way or that way and it really doesn't matter because the overall intention is communicated, there are more targeted and effective ways to use these tools for all children, and some children really need that extra step (and, interestingly it is rarely distinctions like whether a consequence is "natural" which matter). It's also a helpful marker because if it doesn't work, then you have something specific to say e.g. "The methods from the Incredible Years course aren't working for him".
FWIW, nursery and school never ever flagged anything up for my eldest who is now diagnosed. For my middle one who is in assessment now, I had lots of complaints of disruptive behaviour and lots of puzzled meetings but any time I mentioned ND they were all full of "Oh no, no, definitely not!" until I eventually said there is a family history of ADHD and then suddenly they totally did a 180 turn and it became highly likely
He was also slightly behind on developmental assessments at age 4 and 5, though we wouldn't have had those in the UK. Mainly behind because he wouldn't cooperate with the assessment
although he also didn't understand some of the questions/instructions which he apparently should have been able to.
My eldest - I really wish I had understood him better younger, because I think our relationship sustained a whole lot of damage because of how difficult, frustrating and impossible I found his behaviour. It got better again but I felt terrible about it for years and I felt it was my fault.
FWIW, all or most of the resources which have been helpful for us have not been diagnosis specific. And while everyone recommends The Explosive Child, I have also seen lots of people have the same reaction that you have had to it. There are good things about the approach, but I don't think you're in the right place for it to be helpful at the moment. It gets suggested first because it's been around for a long time but it's very radical and not a useful first step into alternative parenting approaches, IMO.
You say he is high energy, and lots of people are suggesting ways to help expend his energy which should be good. Usually when children are being boisterous with toys, people etc giving them an outlet for that energy helps. And this contains a lot of jargon but is a good one to save if he is very physical (it's about different physical sensory inputs): https://www.occuplaytional.com/2023/12/04/a-proprioception-primer/
This (free) course is the kind of thing which is helpful in terms of honing those ordinary/everyday kinds of parenting approaches into a more effective version of all the good stuff you're already doing. I like it because each section is short and likely builds on stuff you're doing already, so it's really easy to integrate into everyday life and it is surprisingly effective, although more so for my 3yo than my 6yo. (It works for him too but not quite as easily). https://www.coursera.org/learn/everyday-parenting/home/welcome
Most underrated parenting book ever - When Your Kids Push Your Buttons.
The Whole Brain Child might also be good, by Dan Siegel and Tina Payne Bryson. That is about brain development/neuroscience and how it can affect behaviour and parenting approaches. Very accessible.
Lastly this presentation is absolutely packed full of suggestions/info and is really well done for anyone who is parenting a child who has a real need for attention/intensity in the way they seek attention. I love it and share it a lot and do use the ideas from it. I wish I had had this when DS1 was younger.