I've been looking for that one too and did not find a way to turn that notification off. At least, not yet. I'm on Android 12 and they tell me like once a week which is an incredible waste of my time.

@Robert, the phone prevents connections from the outside in. How would a push be implemented? Would it use a Google Pub/Sub service the Android can connect to?

The "SMS Backup & Restore" app. has such an option indeed. It's under "Tools" as "Delete messages or call logs". You could delete nearly all of them in one go. It left the last 15 messages in the list.

Okay, I had the opportunity to test with AndFTP which you proposed above and it worked as expected! Much faster. So I guess PowerFTP is rate limiting you (at least the free version) even though their info doesn't say anything about that...

Do you have proof of that? I can't find anything other than your answer which would confirm your statement. It's not that I don't believe you, but I would think that they would mention it somewhere if that was the case?

Okay, I have iperf3 installed in Termux, I'll check with that and report. Otherwise I added some info about my network. The WiFi is on the LAN as far as my PC is concerned.