I agree that the right to distribute and alter software is really important for our freedoms online.
However, switching.social is aimed at non-technical people. To them, "free software" just means free-of-charge.
If I say free software is a good idea, then they will think any app that costs €0 is ethical 😟
First, it's not just about distributing, it's about 4 freedoms: https://fsfe.org/freesoftware/basics/4freedoms.en.html
Second, non-technical people have no idea what "open source" means either, so you might as well be using the right term to educate them.
Third, you can capitalize Free Software to make it more obvious, or call it Libre/Free Software, or FOSS, etc... there are many options.
Open source is really bad because it does not imply any kind of freedom for the end user.
Generalistic and moderated instance.