Leaving UK after Skilled worker visa

My skilled worker visa will expire next March and I can’t/ don’t want to renew it/ apply for a new one. I’m from Europe. Where can I find the official information about how long can I stay after my visa expires? I read articles about 30 day, 90 days but also that I have to leave until it’s expires. For an European it’s 6 months what we can stay in the uk without any visa for travel but I donno what is the situation after visa expiration. Do I need to leave the country asap and I can come back and spend a few more months? Or I don’t need to leave Uk and I can spend extra 30 / 90 days? Please send me links/ experience if you know more about this, thanks.