Desktop and Mobile website

I am having difficulties keeping websites set to desktop or mobile website. It used to magically keep it how I wanted either desktop or mobile without having to request one or the other. Now when I use Facebook it keeps reverting to mobile and when I request desktop it doesn’t recognise that it is on mobile so I have to request twice for desktop.

It appears now I have to go into settings and select safari and request desktop for all websites and manually request mobile for sites that have a better mobile site like youtube and Wikipedia. If I leave it as do not request desktop for all websites it makes every website mobile and for the garbage mobile sites like Facebook and Instagram I request desktop for that website. But when I click on a link it reverts to mobile.

It is frustrating and I want to know why it is suddenly doing this, also it messes with my ad blocker because it doesn’t work on some mobile sites.

Thank you for reading my long-windedly confusing explanquestion.