I don't know exactly what you would call it, Fake look - Fake orientation - Head Lock - Orientation Lock. Basically just a workaround for flexible block placment orientation. Instead of requiring server side support you can instead do the following. For example you look straight up then activate the tweak, now whenever you move your head it will only change client side and you can move freely around placing blocks in the right direction (on the server or other players you will be still looking up) and whenever you stop the tweak either return the player to the orientation they were orignally or just update to the server. This could mess alot with anit cheat especially with sprinting backward and hitting in other directions. A workaround for this could be that the player heads moves normally but whenever you place a block it 1- puts the client in that orientation 2- places the block 3- returns the player to that orientation (all of that only server side and the client wouldn't see their head spinning around) I didn't suggest this second workaround first cause it looks a little "hacky". But I guess you would know more than me on what to do, I would love to hear your thought on this if its possible or not or any other points.
I don't speak english so if any point I said wasn't clear or is completely wrong I am sorry

There is a fallback mode planned for the flexible placement features that would fake the player rotation as part of the placement action. But because it needs a delay between the player rotation packet and the item use packet, I'm not sure how well that would end up working in practice.