I'm a Gnome user so can't speak to KDE, but on Gnome GSConnect is pretty good. It definitely has much more of a open source/hacker feel to it than I'm sure the Apple experience does, so that part may be disappointing, but the features do all work pretty well. When you're on the same LAN it is also lightning fast. I often get a notification on my laptop that I have an incoming call before it even starts to ring.
Big limitation there is that there's no server sitting in the middle, so they have to be able to speak directly. Obviously not a problem at home or on the same wifi, but if you want it while traveling then you can add something like Tailscale or similar. Very, very easy to get setup and works pretty well. It does introduce a lot more latency than I'd like depending on where each device is, but it's very usable.
I would also definitely take a look at scrcpy[1]. It's really a killer app that lets you connect nearly everything on your phone over adb. I use it via USB, but it works just fine over wireless adb as well. You can forward audio, video, clipboard, and much, much more (for example, you can use your laptop keyboard and/or mouse to select thing on the mobile).
All in all it's likely to be a step down in some ways, but probably a step up in others (unless there's a scrcpy equivalent for mac/iphone). The freedom you gain though more than makes up for it IMHO.
[1]: https://github.com/Genymobile/scrcpy
