Just some pointers to more context. There has been a lot of discussions about the new syntax here and at GitHub.
An if-then-else wikitext syntax has often been requested by standard users, since they consider nested $reveal and $list constructions unintuitive and complex.
The problem with <$list></$list> <$else></$else> format are discussed in details at GitHub. Starting with an initial PR, which was incompatible with Evan Blaster’s “condition” plugin. So it was rejected. Evan Blasters “condition” plugin is brittle, that’s why if-then-else was implemented in the way as it is now.
The merged implementation ist at: Conditional Shortcut Syntax by Jermolene · Pull Request #7710 · TiddlyWiki/TiddlyWiki5 · GitHub
There is also a long thread about the proposed syntax from end of August 2023 here at Talk