I want an option to move or copy a picture tube to a category and to create categories myself.
Here is a work around for what the OP wants:
1. While viewing the choice of tubes click the middle button at the right - File Locations
2. You should find a User location for your version of PSP - Copy that address. (I have added links to other locations for earlier versions where I added new tubes
3. Open File Explorer and paste the Users link into the address bar.
4. Use the usual explorer features to create new folders / categories and move or copy tubes into those folders.
5. As you can see I used category 1 and category 2 . They appear at the bottom because I used lower case . By changing the first letter to a capital they appear higher in the alphabetical list.

- 02Added categories.jpg (62.73 KiB) Viewed 752 times
Others may be able to describe different ways to add and change picture tube folders.
Systems XP, Win7, Win 8.1,Win 10 Version 1607 Build 14393.2007 & version 1803 Build 17134.285