I first tried "r", then I unbinded the same key used in jei so that only tool belt is using the key "r" but still doesn't work. Finally, I tried bind it to another key that is not used by anything. But still not working. Please help if it only happens to me.

Sorry, it suddenly works. I don't know what's the problem. But this problem appears when I first use it in RLCraft(1.12.2) as well. Quick switch is not available for a few minutes when I first start up the mod(craft the first tool belt).