Linux

Yes, the scaling sucks in LMMS and I don't think the devs care to fix it.

It seems LMMS hasn't been updated for two years, which might imply it has become abandonware. This is bad, because it means it's not built to use modern libraries, which features updates to things like fractional scaling and cross-display scalability. You can still use it with PipeWire (the new audio server for Linux that's replacing JACK2 and PulseAudio), but it's not a "first class citizen" in that regard.

Before reading my huge aside, have you tried setting scaling factor as a launch variable? Here's a StackOverflow answer that shows you how.

In any case, I could recommend some alternatives since LMMS does seem to be abandone, PipeWire is the new shiny and that people are generally sunsetting X11.

Ardour is probably the most accessible of the open source DAW's, but it does not have a pattern sequencer that you find in LMMS. But, learning how to edit MIDI and using keyboard shortcuts will help you to compose more easily.

MuSE was originally a tool made for composition and orchestration, but blossomed into a fully featured DAW. It's written in QT, so it should be blazingly fast.

Traction is semi-proprietary, in that the engine itself is open source, but the applications are not. Traction Waveform Free is available though and it's gotten quite polished over the years.

Zrythm is the "new kid on the block", but has blossomed into a fully fledged DAW. It's GTK based, so if you're using GNOME it'll work nicely with Wayland. It's also copy-left, so there's little chance it'll go down the Audacity route (traitor!)

Bitwig is proprietary, but a fantastic fully featured option. It comes with a slew of MIDI effects, audio devices, synthesises, samplers and samples. Similar to LMMS it comes with a built-in sequencer that allows you to create loopable clips instead of copying and modifying MIDI clips all the time, which you play and record into arrangement. If you'd like to use your DAW in performances, this is probably the best option. Essentials cost $99, producer edition costs $199 and the full studio edition $399. It may seem expensive, but Bitwig is a professional DAW with all the bells and whistles. They to provide a demo for you.

I'm sorry if this was a bit of a sidestep from your issue, but the alternative of course is that you can try to contribute back to the GitHub repo or fork the LMMS project to add the features or fixes you want. That being said, Wayland is usurping X11 and soon both GNOME and Plasma will be going Wayland only. So I'm throwing a bone here more or less. At some point you will be forced to make the switch, or adhere to outdated software.

The choice is yours of course. Happy beat making!

I remember managing to get this issue solved on my computer. Looks like a QT issue. I may not remember exactly how I fixed it, but try the solutions in this thread and see if it works: https://lmms.io/forum/viewtopic.php?t=34104

In particular run export QT_AUTO_SCREEN_SCALE_FACTOR=0 and then run LMMS from the same terminal.

Also in response to other comments, LMMS is actively being worked on (though updates have been slow) -- the last commit on the master branch was from 3 days ago, so that suggests that the project isn't abandoned but development's just rolling slowly.

I've had this issue with X11 on GNOME in recent releases as well. Blender probably does this too if you haven't checked.

Do you have scaling turned on in display settings?