I did little research and I found an answer:

Yes, an EU citizen can set up a company in the UK after Brexit. Online platforms for company registration can be reliable, but opening a bank account may be more difficult as most banks require identity and residency proof. Online company formation services typically handle the company registration, but additional effort may be needed for opening a bank account. Running an online business in the UK post-Brexit is possible, but you should be aware of new regulations regarding trade with the EU.