With the release of ArcPro 2.9 a new toolbox format appeared (atbx). It does not allow users to create metadata for a tool (e.g. model parameters) to enable documentation. It also drops any existing metadata from a legacy toolbox model tool.
Although this new format has improved performance I certainly can't use it as it is, as I need to document my tools interfaces.
So the idea is simply enable metadata creation for model tools in this new atbx toolbox. I've not tried but I assume script tools will suffer the same fate?