I think I need to open an ISA if I'm going to do this long term. I assume it will negate the 'blow' somewhat like with the CGT I had to pay for the GME shares
Make sure you do it before the end of March so you can use this year's allowance.
Dump your 20k in, and anything you do with that account is exempt from CGT, even if the value of the portfolio grows well beyond that 20k.
Bit daft to not have used a S&S ISA for a GME YOLO tbh if you made more than 12k!