SUMMARY
When network manager changes state, e.g. connected or disconnected to a wired network, then panel freezes until state change finished.

STEPS TO REPRODUCE
1. Open network applet
2. Select wired(?) network and connect or disconnect to it
3. Panel freezes until network manager connects or disconnects

OBSERVED RESULT
Network manager might connect or disconnect instantly or take some time.
When it takes tome time, panel freezes.

EXPECTED RESULT
Panel does not freeze

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.22.90
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.11-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-4790K CPU @ 4.00GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 4600

ADDITIONAL INFORMATION
I've observed this for a long time, so it's not a recent regression. I'm not sure if it ever worked without freezes.