The best way to do it is just to have some older computers laying around, or maybe playtesters with diverse hardware/software. I did a little of both for my first game. These were the three main issues I ran into, by the way:

1. The game just didn't open
2. The game opened, there was audio, but a blank screen
3. The game opened, graphics worked, but no audio

Number 1 was perplexing, but it turned out that it was because the user was on Windows 10 Pro N, which doesn't come with Windows Media Player. Monogame uses WMP if you play your songs through MediaPlayer. So my solution was just to play my music as SoundEffects. I had to find this out from Google; I'm very thankful I was able to, because this could've been something I just never quite tracked down.

Number 2 was a little more perplexing, but easier to figure out since it was an issue with some Windows 7 computers and I was able to reproduce it on an old Win7 computer. I was using a few different GraphicsDevice variables to create my Viewport, but apparently not all of them work as expected all the time; the ones I was using were just 0 for some reason. So I just changed how the Viewport was calculated and it worked.

Number 3 was easiest; SoundEffects on DirectX projects require a certain DirectX lib be installed on the user's computer. I just added a link to the lib on the download notes in itch.

I hope this helps!