I personally use KDE Connect ([1]) on Linux; I use GNOME on my computers but luckily there's also a shell extension that's compatible with the protocol which integrates nicely with my desktop [2]. There's also a Windows binary available [3] that supports most features I believe.
This tool allows for file sharing/browsing over LAN/WiFi as well as sharing notifications (including quick responses), remote keyboard support, integration with SMS messaging, and all other kinds of cool stuff. For example, KDE Connect also pops up a media player control window notification on your phone if you start playing a video in your browser, which is super useful because now my smart watch can pause my browser. Everything is end-to-end encrypted through (basically) standard SSH so you're not relying on cloud stuff to make it work.
Android has nerfed keyboard sync (no background access to the clipboard without rooting your phone unless you're Google or the manufacturer) but there are other benefits as well. I rooted my phone just to get this feature back and I've got to say that copy/pasting my TOTP codes makes 2FA so much easier to deal with.
Apple devices aren't as well-supported yet as the restrictive app store policies and lack of developers were a problem for the KDE folks for a while. The iOS version has recently picked up some speed and I see there's a macOS version as well now, so if you're on those platforms you could give it a go and see what happens.
[1]: https://kdeconnect.kde.org/
[2]: https://extensions.gnome.org/extension/1319/gsconnect/
[2]: https://apps.microsoft.com/store/detail/kde-connect/9N93MRMS...
