Fractional scaling below 100%

I have a laptop with a 14" screen at 1920x1080 resolution and an 17" external monitor with a 1366x768 resolution.
Certain applications don’t scale well on the external monitor: Thunderbird is an example.
I’m happy with having my laptop screen at 100% scaling and would like my external monitor to scale at, say 70%, but this is not possible in Display settings.
I read somewhere that you could modify the ~/.config/monitors.xml file to adjust the scaling manually. I tried doing this, but, instead of getting the intended result, ended up having the laptop screen scaling increased to 125% and the external monitor’s to 100%.
Is there a way to get the intended sub-100% scaling on just the external monitor?

Added fractional-scaling, mixed-dpi

I think if you would scale below 100% on the other monitor you would lose pixels, wouldnt you?

Also, Wayland or X11? You can find that out in the settings.

As a “last resort”, KDE Plasma allows using different scaling out of the box.

I’m using Wayland.
I don’t want to move to KDE: I don’t like it.
For some reason, this issue doesn’t happen with Windows.
That being said, I asked a different issue regarding Thunderbird on different monitors. It is the main programme I cannot use on the external monitor because of the scaling difference.

Could you solve this issue? I’m facing exactly the same problem and it’s driving me crazy. Did you end up switching to KDE?

I didn’t solve the issue. I tried KDE in the past and I didn’t like it at all. Gnome remains my favourite Desktop environment in spite of this issue.

My solution was to scale to 125% the laptop monitor and just let the 1366x768 be as it is.

COSMIC can do sub-100% scaling, and it’s closer to GNOME than KDE. Technically still in alpha, but it’s already quite usable.

I thought of that, but I’m happy with 100% on my laptop screen.

Have you tried wdisplays ?
In general, under Gnome it is much better not to scale screen at all (leave at 100%), and use instead Tweaks-> Fonts → Scaling Factor
This allows also scaling lower than 1.

Using font scaling factor makes the text smaller on both screens, but the UI stays the same. This opens 2 new issues:

  • By making the text smaller on both screens, one screen ends up having tiny text and the other normal text.
  • Since the UI doesn’t scale with the text, the buttons and the headerbars look way bigger than the text they contain.

When I try to use wdisplays I get the following message

Compositor doesn't support wlr-output-management-unstable-v1

Not at all. The UI scales accordingly with the text, that is precisely the reason why I gave you the advice. If it doesn’t there is something wrong with your setup. Just played with the scaling from 1 to 1.95 on F41, F40 is the same, as well as several F3*.

I took the exact same screenshot three times to show you that the UI doesn’t change at all and it’s just the text:

UI at 75% text scaling:

UI at 90% text scaling:

UI at 100% text scaling:

I didn’t tell you “I don’t believe you”. I told you there is something wrong with your setup. You didn’t provide any info, not even which Fedora it is, which Gnome shell version etc.