Are you possibly talking about UK brokers with FIX API?
You can find some brokers of that kind right here: https://fx-list.com/forex-brokers-uk
Check box 'ETFs' in the 'Platforms' filter, that would narrow down your search.
Too much people started to farm bitcoin, Too much alternative coins appeared. I don't think bitcoin is finished... but it certainly going into a slumber right now...