Quiet Air is a server-side mod that hides this message from the server console and log files: Player <name> standing on air - force-sending blocks below

Vanilla Minecraft prints this message often and it is harmless. Quiet Air only hides the message. The server still resends the blocks, so gameplay does not change. Other log lines and chat are not affected.

This log message is considered a bug (https://bugs.mojang.com/browse/MC/issues/MC-311727) and should be fixed in 26.4