According to HMRC, withdrawing funds from an ISA is considered a ‘self-transfer’ and an ‘investor error’. Instead, you should transfer the funds to maintain their tax-free status. This applies both if you transfer from or to Trading 212.
You should also note that Trading 212 ISA is not ‘flexible’. This means that withdrawn funds will not reduce your used allowance. Depositing money elsewhere can lead you to a disallowed combination of ISAs or oversubscription. 👌