Ey,
Today I went outside for a test ride and everything worked how it was supposed to be.
For me, it was also unclear if the 4iii was compatible because every review said it wasn’t.
However, for me the 4IIII PRECISION 105 R7000 POWER METER LEFT (4/2020) is working on the Polar v650 (v1.5.5).
I hope it will help you and everybody else that needs this answer.
If you have any questions, feel free to ask.