I'm a hobbyist digital artist and have had to do a handful of graphic design projects for my mundane, non-art-in-anyway job.
As our computers are locked down Windows PCs, I've had to manage with MSPaint. It's always taken me double the time as on any other program or app, and I have been wishing it had layers for years.
Since this update is Windows 11 only, I'll have to for my company to upgrade, so I can look forward to layers in maybe 5 years.
Take a look at PhotoPea then. Needs nothing more than a browser. Runs fine in Edge and can be installed as PWA. That should work fine even on a locked down machine.
I've never experienced this, I've only experienced that you cannot do anything you need an admin for, maybe the control panel and settings app were removed from sight.
Try Paint.net. Layers, transparency, filters and even plugins. It's free to download from their website. Install from Windows Store does have cost as a way to donate.
When a computer is locked down by an employer it doesn't just mean you can't install software, it means that you CANNOT RUN software that isn't approved.
I've found that level of locked down to be rare, usually portable apps still work. That being said running portable apps is still risky since it's likely against company policy and could be logged by IT.
Are you able to use WSL under Windows? Combined with something that can display X11 graphics (such as MobaXterm) you could pretty much use whatever Linux-based software from within the windows environment, including stuff like GIMP which does transparency and layers etc just fine