Most emulators are free software and work on Linux and have worked for a long time. As Android and Raspberry Pis have become quite popular as emulation systems, the free software emulators, which are easily portable to these ARM+Linux system, have taken off as the most popular emulators in general. Anything that’s also available on Android or RetroPie will work on Linux for sure. There’s an emulator for every popular console that works on Linux about as well as it does on Windows.
DOS games you can run in DOSbox. Pretty sure compatibility is 100%. This is also how e.g. GOG makes these games run on Windows, because modern Windows can’t run these games either without emulation.
As for old Windows games, it is worth trying Wine, the Windows compatibly layer. Volunteers have successfully been trying to get games (especially games actually!) to run on Linux since the 90s. Twenty-something years ago I was gaming on Linux playing Starcraft, Half-Life, Counter-Strike, Diablo 2, Warcraft 3 and god knows what. Anecdotally, some old Windows games that no longer run on Windows will work fine in Wine. A prominent example is The Sims 2. There’s a video out there of some millennial Sims streamer and housewife instructing her thousands of viewers on how to install Linux in order to get that game to run better.
Steam comes with a version of Wine, called Proton, so 90%+ percent of games on Steam run somewhere between fine and perfectly fine. Not everything though, you should check on protondb.com.
Playing in a VM is a terrible idea btw, the performance will suck. You don’t need to and don’t want to do that.
Brave is proprietary, and they have some sort of ad scheme to make money. Also the head of that operation is a known homophobe.
Mozilla are bought and paid for, controlled opposition. And everybody working there has about the same worldview as your average Facebook employee.
LibreWolf is just a couple of tweaks to Firefox to improve the situation a little bit. So let’s say there is no good option.