Something as simple as a slide out menu needs JavaScript and couldn’t really be done server side.
I’m not trying to tell anyone how to design their webpages. I’m also a bit old fashioned. But I stopped making animated gimmicks many years ago. When someone is viewing such things on a small screen, in landscape mode, it’s going to be a shit user experience at best. That’s just my 2 cents from personal experience.
I’m sure there are examples of where js is necessary. It certainly has it’s place. I just feel like it’s over used. Now if you’re at the mercy of someone else that demands x y and z, then I guess you gotta do what you gotta do.
I second smbsync2 for phone backup. It’s very customizable and once setup, just works.
I also use syncthing but only for syncing files I want to be the same on all devices. FreeTube watch history and subscriptions, stuff like that.