Add fractional scalings of 250%+ to accomodate high DPI displays

Is your feature request related to a problem? Please describe.

On high DPI screens (e.g. 14 inch 4K, even 16 inch) graphics still looks too small IMO at 200% scaling. For 16-17 inch laptops 1080p is IMO too low, 4k is about standard.

Describe the solution you'd like

To add scaling options of 250, 300, 350,,400, 500% to display's setting (there is a row of 5 in LM21, please add another with additional 5).
Alternatively add 250% and 300% for one row Cinnamon already have (not future-proof IMO but settings window might look better and height of the window is not increased).'

By the way, is there dconf (gsettings) to set fractional scaling? Could not find one. If not, please add.
TIA

Describe alternatives you've considered

Sticking to 1080p 14 inch, works personally for me now but why not make such great desktop environment more future-proof and more convenient for others?

Additional context

I was positively surprised at LM 21 scaling, looks good on my laptop, thanks to the developers!

I don't know technical details. If any scaling now is just a matter of putting different number in a variable and changing setting window in GUI. Or each % require fine-tuning. In latter case I suspect my request is not easy to do.

The issue names no files, tests, or entry points; start by tracing Cinnamon's existing display-scaling settings and whether they are exposed through gsettings. Done would require agreed support for the requested 250–500% options and a documented way to configure them, with the display settings UI reflecting the supported values.