Looking to invest..

Hi I was born in the US but moved to London when I was 7 so I have dual citizenship. I’m 20 currently a student and have only ever held minimum wage jobs that pay too little to be taxed. I have some money saved up and was looking to start investing but every-time I attempted to open a brokerage account I was denied because of my American citizenship.

What are my options for investing this is such a weird position to be in. I had no idea as an expat there would be these implications.

Would anyone also recommend forgoing my US citizenship?