Adobe flash in 2021 and beyond!
1) Download the "Flash Projector" (which is basically just a standalone version of Flash Player)
from the following site: Flash Player Debug Downloads
You can also download it from here (needs to be unzipped to be used)(if you download it from the following link, unzip the file and skip to step 3.): Flash Player Debug Direct Download (trusted mirror)
2) Click the one labeled Download flash projector without anything else added to it

3) Open the program you should see a blank white window,
with a few options at the top
4) Goto File -> Open

5) Enter the direct URL to the main swf file for whatever game you want to play-

Direct SWF Urls: