I think I'm right in saying that the Photoshop Elements license is for one individual user. After installing it on your primary computer, you can install Photoshop Elements on a second laptop or desktop computer as long as Photoshop Elements isn't used at the same time on the primary computer.
In the scenario you have described, you would be infringing the license agreement if you installed Photoshop Elements on two computers with two different users using Photoshop Elements at the same time. You would need to buy two copies of Photoshop Elements 2021.
The license allows for two separate installations to accomodate the fact that some users own both a desktop & a laptop and would like to use Photoshop Elements on both machines, but not at the same time.
As a side note, you might want to take advantage of the current 25% off deal that Adobe USA is running on Photoshop Elements until April 11th, which brings the price down to $74.99 per copy.