Comment # 1 on bug 1227124 from Alynx Zhou

As you say, fractional scaling is still an experimental option, so it may or
may not work correctly...

Fractional scaling is a limitation of old X apps, currently this option is an
workaround. As you say #3567 may fix it, but it needs to be merged and I think
it still requires apps to support scaling itself.

This is still an upstream issue and the upstream MR seems still under
development, I would suggest to focus there for progress.