Section
You probably came to this page because some elements of the UI are disabled / grayed out as seen in this picture:
Explanation
This is because add-ons do not support all the features Java mods do. In fact, Minecraft Bedrock Edition Add-Ons support a very limited subset of features by their design.
We support most of the features and plan to add more features when support for them will be introduced in the add-ons system inside Minecraft.
Workspace type notice
This is also indicated by the warning when making a new Bedrock Edition Add-On workspace. This message should not be ignored.
A similar problem can also occur with other workspace types and generators, depending on the feature set they (can) support.