@Juejue thanks!! 😊 it's kinda hard to explain so I'll try my best.
my keychains are double sided, I make both sides as I would a bracelet and then fold them in half with a keyring in between.
To make the ending I turn the keychain sideways so my leading string is on top (instead of left/right side as normal). then I gently pull on it and make fb or bf knots with base strings on a leading string - just one knot with each string. It requires some trial and error to figure out the tension and which type of knots to make. That way the base strings kinda turn inwards and get hidden in the inside of the keychain when it's folded. You can put some glue/nailpolish on the knots and trim the base strings close to the knots so it's less messy. As for the leading string that sticks out after you do all the knots with base strings - you can either put some more glue on the last knot and cut it really close or glue it on the back side of the keychain and it gets hidden when folded.