Robinhood was planning to launch in the U.K in 2020. But it looks like they have abandoned those plans. Thankfully if you're looking to invest in US stocks without paying any commissions, there are a couple of good options- eToro and Stake.
I currently use both of these platforms. I use Stake to invest in ETFs and I use eToro to build a portfolio of tech stocks (like Apple, Tesla, Netflix, Amazon etc).
Here are my favourite Robinhood alternatives: