ETF Germany

Hi all, bit of a hypothetical situation but you don't know what will happen in the future, lets say in 30 years time my ETF portfolio is worth 1,2m with 400k being unrealized gains, what happeneds if i moved out of Germany to lets say the UK lived there for 3 years until I retired (UK is my birth country) and then sold my shares? uK has a lower capital gains tax (sometimes 0% through a loophole of 20k in an isa) would i have to sell my shares before i move from Germany or would i move, retire and sell them and then pay UK capital gains tax which is lower? I know germany has an exit tax but i believe thats for business owners and is 1% of a company and not relating to ETFs.

Has anybody moved and sold shares in another country that were bought in Germany?

Thanks