I want to enter the US and UK markets, but I don't know where to start. SEO or PPC? What will give faster results? Maybe someone has already promoted business in these countries?

It all depends on your goals! If you need fast traffic - PPC, but for the long term, SEO is the best choice. I worked with an agency that deals specifically with international promotion, and they https://www.seotm.com/services/international-seo-ppc/usa-uk-australia.html helped me take good positions in Google. The main thing is to adapt the content to the local market.