Calculator : Arity from F-Droid
(I tried Calculator from F-Droid, too, but it’s really basic. When I seldomly need a calculator, I want to have some advanced stuff. I didn’t try Simple Calculator from F-Droid, because it looked pretty basic on the screenshots, too.)
Calendar : Simple Calendar Pro from F-Droid
(I don’t work much with the calendar, I just sync my few calendar events from Thunderbird to it … I tried Etar from F-Droid, too, and it would work for me as well.)
Camera : Google Camera with HDR+, Nightsight etc. (Xiaomi Poco F1 port) from XDA
(I kept the original Camera App, too, for the moment … can’t decide just now whether to omit it or not.
A well-known and widely used non-Google camera App would be Open Camera from F-Droid.)
Clock : Simple Clock from F-Droid
Contacts : Contacts 1.7.31 by LineageOS from APKMirror
(I tried Simple Contacts from F-Droid, but it can’t put shortcuts of contacts to the home screen, and I absolutely want to have that. Furthermore, one out of two times I tried it, Simple Contacts couldn’t see my contacts when Dialer and LineageOS Contacts could … weird.)
Dialer : Lineage OS Phone 19.0 by LineageOS (Variant: September 21, 2018) from APKMirror
(As Emerald Dialer from F-Droid seemingly doesn’t cut it yet.)
Files : Ghost Commander or Amaze from F-Droid
(There’s still a use case for Files, though.)
Gboard : Simple Keyboard from F-Droid
( Attention! This will not work with a password as unlocking method, use a PIN instead .)
Gmail : Email 9 by LineageOS from APKMirror
(I tried SimpleEmail and FairEmail from F-Droid, both pretty similar K9 forks, but I didn’t like them.)
Google Chrome : Fennec F-Droid from … well … F-Droid
Google Maps : OsmAnd+ from F-Droid
(In case of need Google Maps has a usable website.)
Google Play Store : Aurora Store from F-Droid
(I deactivated the Play Store since Aurora got anonymous login to the Play Store back.)
Launcher : Lawnchair from F-Droid
(I tried Trebuchet from XDA, too, which would work for me, too, but with F-Droid there’s at least a way for automatic updates, even if there are none in sight in this case for now. I didn’t uninstall the stock launcher yet.)
Messages : QKSMS from F-Droid
Music : VLC from F-Droid
Photos : Simple Gallery Pro from F-Droid
Videos : VLC from F-Droid
YouTube : Has a usable website.