After upgrading Plasma to 6, networkmanager package "does not exist"

When I open the networkmanager widget from the KDE panel, I see “Error loading Applet: package org.kde.plasma.networkmanagement does not exist.” I recently declaratively updated my system from Plasma 5 to 6, and after that somewhat manually[1] changed my UID from 1001 to 1000. My config is here[2]. Searching the git log for changes involving the string networkmanager (git log -p -S 'networkmanager') shows no such changes for more than a year (and I’ve made 35 commits since). Google and this forum both give no results

So … ideas? Thanks in advance.

[1] UID declaration is ignored after upgrading Plasma 5 to 6 - #7 by JeffreyBenjaminBrown – thanks, @rhendric!

[2] nixos-experiments/config/configuration.nix at 1b7d50d0ba6d76cb4938f836d8573f66201fd622 · JeffreyBenjaminBrown/nixos-experiments · GitHub

It’s gibberish to me but there’s a similar issue on the OpenSUSE forum: