Can the Fairphone True Wireless Stereo Earbuds be used with more than one device?

You can do that, but you cannot switch the source from the (Fairphone TWS) earbuds themselves. You need to activate/deactive the connection device ↔ earbuds on the source device.

I have been able to make the earbuds work with all the FP1, FP2, FP3+, a (now almost 14 years old) Mac and a Windows Surface:

I now mainly use my earbuds with my FP3+, but just yesterday used them on the old Mac again (works a bit wobblier though, probably because of the old Bluetooth standard on the Mac).