We took my son outside today to bike around with his training wheels and I took them off for a little while and he practiced learning how to keep his own balance. I would wait until he seemed pretty centered and then let go of the seat. But there’s really no in between. You’re either leaning on training wheels, or being helped by someone else who’s holding you up, or you’re on your own. And if you’re not practicing on your own, it’s impossible to learn what you need to learn.
Are you leaning on anything that you could try letting go of? It might be scary, but it might be worth it. Leaning into a turn feels different and better on a bike than it does on a trike.
And remember: You’re going to fall. The only way to learn how to keep your balance is to learn how it feels to lose it.