Unable to open project to a different version

Question

I have two versions installed: 2017.2.2 and 2016.2.6.

I am trying to open the project in 2016.2.6 in the project launcher, but the option is not available (doesn't even show up), and will only open in 2017.2.2.

2016.2.6 is a locally installed version while 2017.2.2 is installed via the launcher.
Both of them show up in the versions installed page.

What do I do?

Comments

Also interested in this, having mistakenly created a project in a later version that is not supported by the game I need to use it in.
Is there any way to export any of the work back to the older version, or do I have to start from scratch?
(2021.1.10 > 2019.25)