It just puts a black shade then goes back without anything
How many times have you tried? it might be because ROBLOX thinks somone is breaking into your accound give it some time if not then contact support
Retry with a VPN. If it works with only a VPN, Roblox is probably blocked there.
I had the same issue and just fixed it. Make sure your iphone is up to date(software update). I updated my phone then shut it down completely for about 20 seconds. I actually used my email to login instead of my username(after updating my phone ofcourse), try that.
it def is not stolen cuz im still logged on my computer
No, roblox thinks you are a hacker and are trying to break into your own account