Just checked the history on this one. It as working back in August 2020 which was when the offsets were marked as working for read/write. Then there is your recent report, where it was reported as not working. I investigated and found the sim rate was being momentarily set but returning to 0 afterwards, which is causing the issue.
I’ll report back in the FSUIPC forum topic once I’ve had a chance to look into this in more detail.
For reference, its here: FSUIPC7 - HOT KEY to set the sim rate to 1 (256) normal - FSUIPC7 MSFS - The simFlight Network Forums
And the original report of sim rate offset read/write working is here: SIMULATION RATE Not reading - FSUIPC7 MSFS - The simFlight Network Forums
John