

i havnt tried it but librera on android has a sync option that uses google drive
https://librera.mobi/faq/setting-up-synchronization/
i think it only does highlighting in pdfs though.
for other things like epubs, you can select text and then bookmark it, you can add in your own notes to the text, but they are mainly used for navigation. when you add a bookmark first, the text is visually highlighted but it goes away as soon as you scroll and i dont know if theres a setting to keep it highlighted
after using jellyfin and emby for a long while ive gone back to basics, just local mp3s synced between devices using syncthing
something like KDE Connect might work for remote control as long as you are able to install it on both devices