Unable to set fractional scales by manipulating environment

In an up to date Windows 10 installation I'm trying to scale a Qt app (LyX) by setting QT_AUTO_SCREEN_SCALE-FACTOR=1 and QT_SCREEN_SCALE_FACTORS=X. Only for integer Xs this has some effect. Maybe it's related to the style (I believe it's Windows Vista, because there is this qwindowsvistastyle.dll in the bundle) since the documentation warns:

> While the macOS style fully supports high-DPI, the Windows desktop style currently has some limitations with certain scale factors. In these cases, consider using the Fusion style instead, which supports high-DPI in all cases.

But, in any case, I'm unable to override the style to fusion and I don't know how to check what styles are available or active for this particular bundle, except for checking what dlls are there (but maybe some styles are builtin and don't require plugins ).

My downstream report https://www.lyx.org/trac/ticket/12060 contains further detail and context.

I'm not sure about 5.15.2 but LyX was recently released so I assume it's 5.15 at least.