Issues after conversion

Hi buffalobillfan !

BTW, the category of an item is not shown anywhere that I could see, which makes it difficult to locate certain items.
There is a setting to bring the categories into the sidebar. But in an item the category is not visible, that's correct.

Only external files can be selected, but I cannot find where 1P's icon library is located.
That's correct. You are only able to upload an external icon file. There is no possibility to switch to an internal icon. You could only create a new item in another category, so it will get another default icon.

It will be helpful for items, such as health card, to be able to add custom categories for items that don't fit any built-in ones.
Actually, there is no possibility to edit the default templates. As a workaround, you could create an item and add / delete the fields you need / don't need. Then use this item as your own template and duplicate it when creating new items in this category. That's what I do when creating new items for Software Licenses.