You can trade as often as you like subject to certain restrictions around day trading - these restrictions are known as Pattern Day Trader rules. Day trading refers to buying and selling the same stock on the same day. Just buying, without selling later that same day, would not be considered a day trade. You engage in Pattern Day Trading if you make more than three day trades over a period of five business days. When trading in the Revolut app, you can see how many day trades you can still make without breaching the Pattern Day Trading rules.
When you open a trading account with Revolut, you agree that you will not engage in Pattern Day Trading. Further details are included in Limited Purpose Margin Account Agreement you agreed to when onboarding with Revolut Trading.