[2023] Chances of updating Unity Engine?

They updated to Unity version 2021.3.16 just last month. Removing bottles was done last June. They have updated to new versions of Unity all along as those versions became stable and once they thoroughly tested each new version on a separate branch created for that purpose.

TFP have modded aspects of Unity so that it best fits their needs just as people mod the game to better fit their needs. Just like an update to the game is likely to break mods and require the mod authors a period of time to get their mods compatible to the newest version of the game, the devs have to do the same when they choose to download a newer version of Unity. There is a balance between how good is the new version for performance and bug fixes for the engine vs how much effort will it be to get the game compatible with the newest version. So far, faatal has been on top of it.