within T212 withthout needing to sell and buy back positions?
No. Investments held in Invest must be sold and rebought in ISA. This is a HMRC rule.
Many other brokers allow positions to be transferred between Invest accounts of spouses. People here have been requested Trading 212 to implement that. Transfer between spouses as a gift is special under UK law because it does not trigger a capital gains tax event and can therefore be useful in balancing out taxable liabilities between spouses.
What about the other way ISA>Invest?
Also has to be done by sale and repurchase. One reason is to establish the new basis cost.