On every shutdown/reboot my computer hangs for 90s and waits for a stop job, which does not happen. I looked into the user processes that are managed by systemd and found localsearch3. If i manually kill that process before the shutdown the shotdown runs normal as expected. I tried to reduce the timeout that systemd is waiting for this process by editing /usr/lib/systemd/user/localsearch-3.service by adding TimeoutStopSec, but that did not help. Running localsearch daemon -k by the user terminates the process as expected, so to me it looks like this stop service never gets called in the shutdown process. If i globally set TimeoutStopSec=10in /etc/systemd/system.conf the timeout is reduced and the process gets terminated after a shorter period of time. But that is not a solution to the root cause.
I don’t know much about these “special” serivces and how they interact, therefore maybe someone tell me how to find the root cause or where the stop job for localsearch gets called from in systemd.
journal logs
I don’t run gnome, so can’t help, but it seems that all file indexing systems are a steaming pile of 
Baloo is the same on Plasma - first thing I turn off.
You can’t uninstall it, from what I have read, but you can limit where it is scanning, might help.
If not you may need to hit it with the big hammer 
(remove the executable bit off the file).