I turned off the internet before using anything, and this particular website was recommended by various people, but it's a good warning.

I have checked the wallet address and can see the ETH that's in that wallet - I just can't load it into MetaMask or connect to it on the Nuri app!

Honestly, it's "just" 150€ worth of ETH, so it won't be too big of a hit. It's still incredibly annoying beccause I'll have to find a different way to convert fiat to crypto and back.