If you look at the Ardour page, you'll see that Ardour (probably with input from Mixbus developers) are working on some very major updates to the core engine.
Totally reconstructing the way to the code deals with time and MIDI time, anywhere to anywhere latency compensation (will be a major benefit to anyone running a hybrid setup) are just two of these things.
You can read more here.
https://community.ardour.org/node/15693
There's no release dates, but I know that Ardour is making headway. Once the Ardour version is released it typically has taken a few months for the Mixbus layer to be added. In the past it's been the standard version a month or 2 before the 32c version. So I wouldn't expect anything this year TBH.
Unless there are critical patches, I doubt we'll see much by way of updates on the v4.x series. OF course, I'm not a Mixbus developer and they could put something out as soon as I post. It's a small developer team so splitting work between the current version (which is very stable) and the new version would slow everything down.
I'm personally very excited for the new version, but am happily working with the current version of 32c for the moment.
That being said, if I can find some time, I will try to compile and run some tests on the Ardour 6 code, my firewire hybrid desk and extensive external MIDI environment would be perfect for giving some of the new features a serious bash.
@jonetsu, why don't you consider using something like XFCE for you window manager, it's a lot lighter on CPU and RAM. I haven't had those issues, but I rarely use non- Harrison plugins anymore, so it might be universal. Can't hurt to try, you can always install XFCE but switch back to KDE if you don't like it.