Mac monitor as display for PC laptop?

That will depend on what available ports the PC laptop has and what monitor exactly you are using with the Mac Studio., as the Mac Studio does not have a dedicated monitor.

If you are using a Studio Display for example, you will need the PC Laptop to have a Thunderbolt 4 or 5 port to use it. If it does not have a Thunderbolt port, then it cannot use the Studio Display.

If you are using a different display, then tell us what ports it has or the make and model of the display and what ports the PC laptop has and we may be able to offer some options.

the official specs for Studio displays require thunderbolt.

Readers have found that it MIGHT be possible to drive such a Thunderbolt display with a USB port, but resolution would be limited.

HBR2, the fastest DisplayPort speed that fits inside a USB envelope, can provide 5K at 30 Hz. If the display falls back to 4K, that can run at slightly faster than 60 Hz without Display Stream Compression.

However, you might be better served by using a more mundane display with your [non-Thunderbolt] PC and re-purposing that high-end Apple display for other high-end work.

...and if it does not work, the Published Specs are what Apple will work to support, nothing more.