SUMMARY
Firstly, finding how to add an activity at all was difficult, because for some reason the create and settings buttons are missing from the panel you get when pressing super-tab. Instead you had to right click the desktop background and click "Show activity switcher", which was hard to find. The super-tab switcher should have the same options. But, anyway, I used that for a bit and then reboot it, but after the reboot the new activity was mysteriously missing from the super-tab switcher, and the option to select activity was missing from the task manager context menu. When right clicking the desktop and clicking "Show activity switcher", the activity is shown as stopped, and I can switch to it from there, but there seems to be no way to resume it so I can switch to it with super-tab. The pages I've been able to find say there should be a play button, but I see no such thing.

STEPS TO REPRODUCE
1. Create an activity
2. Reboot

OBSERVED RESULT
Activity is stopped

EXPECTED RESULT
Activity can still be used

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20201221
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.77.0
Qt Version: 5.15.2
Kernel Version: 5.9.14-1-default
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-4790K CPU @ 4.00GHz
Memory: 31.3 Gibyte of RAM
Graphics Processor: GeForce RTX 2080 Ti/PCIe/SSE2