Can't tell whether ploxiln knew this and was just using it as an example anyway, but the TLS version indicator is dead anyway, the TLS 1.3 specification (passed last call but yet to be published) says to always treat this as though you're TLS 1.2 and marks it "legacy_version" but then you hide the real version number inside a new extension which they aim to prevent from rusting in place.

This was done because the version code ploxiln describes is so thoroughly rusted shut in middleboxes that TLS 1.3 would be undeployable in practice without such a changes.

Also, "fallback retries" aren't a thing. The reason is downgrade protection. If I have a new protocol (TLS 1.3) with better security, but I'm happy to retry with an older protocol (say TLS 1.2) if that doesn't work, obviously bad guys on the path will just ensure my TLS 1.3 connections all fail so that they can attack the weaker TLS 1.2

TLS 1.3 guards against an attacker who tries to downgrade a TLS 1.3 connection, if both sides know TLS 1.3 and yet somehow the packets when they arrive from the client say TLS 1.2 on them, the Hello "random" value sent from the server will have the message "DOWNGRD" scribbled across part of it, and the client sees this and aborts because somebody is tampering with the connection. If the middlebox tries overwriting the bytes with "DOWNGRD" written in them then the random data doesn't match up and the connection fails.