What you describe is (unfortunately) not unusual - and the dongle further limits your options. Rather than buying a full separate laptop/desktop, I would instead suggest a single-use small Win 11 Pro box that is inexpensive, compact and portable, and can be hooked up directly to your Mac as a headless appliance and controlled via Microsoft Remote Desktop. One possibility (out of many) in the MiniPC space would be a palm-sized box like this one:
https://store.minisforum.com/collections/all-product/products/minisforum-em680
This should give you a nice speedup over your laptop (about 25%, I'd estimate), and allow you to use your new Mac for everything else. Minisforum boxes have worked well for me - but, of course, there are many other options/companies in this space.