Which version was this project made in?
You have to know the source version before downgrading — a target only makes sense if it is older than that. Here are three ways to tell, plus one common method that does not work.
Most reliable: ask the person who made it
A project records the software version that created it, which is the most direct evidence of the source version. Asking the other side once beats guessing afterwards.
Next best: your own installed version number
If you can open the project, your version is at least as new as it. The About dialog shows your main version number — Premiere Pro 13.0 is 2019, 22.0 is 2022, and so on.
Unreliable: the file modification date
The date in the file properties only says when the file was last written, which has nothing to do with which version made it. Open a 2018 project today and save it, and the date becomes today.
When you are unsure
Trying every target from the oldest upwards is wasteful. Start one step below the version you know opens it and work down — you will find the boundary in a couple of tries.