Is there a way to connect this Wii controller to Nintendo Switch OLED without a dongle?

You could probably use some sort of adhesive or tape but I don't think that would help them work together.

Maybe hombrew but as far as I know you need some sort of adapter like 8bitdo universal adapter

There's a way. You need a CFW on your Switch. Mission Control supports many other controllers incl. Wiimote.

You can do that?

Wiimotes use what amounts to wifi. They're slow as shit for that reason, so you should probably use an adapter.