The Trading 212 ISA is not flexible, meaning that if you withdraw funds and subsequently deposit back, they will still count towards the current tax year's subscription. For instance, if you initially deposited £5,000 and later decided to withdraw £500, resulting in a remaining balance of £4,500, your current tax year subscriptions would still be considered as £5,000. Any additional funds deposited afterwards would be added on top of these subscriptions.
Note: This is also valid for funds that are transferred between the ISA and another type of account (CFD or Invest).