@Maryamu : you might want to read this post of mine: It gives some details about F-Droid including some other useful apps you can find in the appstore.
I am also using K9 Mail now as my mail-app because it is more practical than the no longer updated stock Android mail app and it also looks more beautiful to me.
Generally there are many Fairphone users who want to escape Google & Co. and seek open source alternatives which don’t limit their users or collect massive amounts of data.