keep seeing mentions of an 'Under 23 side'. Does anyone have any idea how this will work, or if it even actually exists?

Understand how it works higher up the pyramid, with their own league etc. but do clubs in League 1 and 2 have Under 23 teams and how do they work?

There isn't one as far as I know. Don't know why people are conjuring up this idea.

It’s a slightly nicer way of saying reserves.

Scunthorpe tried this didn't they a couple of years ago but it failed and I assume they've given it up now. Really no surprise as players that develop into a league 2 player haven't really saved very much vs the cost of paying them as u23s for a couple of years to develop. And similar players are available on free transfers every year anyway. Amd those that don't quite make it and are only good enough for NL/NLN/NLS don't have any value to be sold anyway.

Teams in the prem can afford to do it because if they get a single player out of it they've saved themselves a huge chunk, and even players that don't quite make it may be worth a transfer fee if sold  to a championship or foreign team. So it can pay for itself.

Having an actual u23s development squad I mean, of players not deemed good enough forbthe first team.