Absolutely! When the new tax year begins (6th April), the tax-free allowance of £20,000 will be reset automatically in your already open Trading 212 ISA and you can keep investing freely. You will not need to open a new account for the upcoming financial year.
If you decide not to invest any current-year funds in the Trading 212 ISA and to move to a different provider, no further deposits should be made towards your account. It can still remain open for you to keep getting tax relief from previous-year subscriptions if there are any available.