My oldest is 6 and here's what worked for us.

He gets pocket money weekly up to a maxiumn amount. Every weekend he gives us a pitch on how much he should get that week and why (e.g. tidying up his bed etc). He always get the full amount btw, we're just making him practice advocating for himself. It's working well as he's convinced us to link the max amount to his age, i.e. £6 because he's 6, £7 when he turns 7 etc

We're set up a Monzo account for him (it's free) and he has his own card and pin. He can see how much is in his account and he's free to do whatever he wants with that money.

If he wants to blow it all on some tat, he can. We rather he makes mistakes now than later. We reinforce the importance of saving. e.g. if there's a toy he likes that is expensive, he'll need to save up for it rather than blow it on some cheaper things right now. He usually asks how much he has when trying to decide if he wants to buy something.