Assign user to new group . reboot needed?

Using Manjaro/xfce I’m logged in as my user. I did this in terminal:

$ su
# groupadd photos
# usermod -a -G photos myuser
# /home/_shared/photos
# chown root:photos /home/_shared/photos
# chmod 3770 /home/_shared/photos

Now myuser should be able to browse the folder /home/_shared/photos using Thunar. I get permission denied. So starting a new terminal session I try (as myuser):

$ ls -l /home/_shared/photos
$ groups
sys network power lp wheel myuser
$ su
# groups myuser
sys network power lp wheel myuser photos
# su myuser
$ groups
sys network power lp wheel myuser photos

So, it seems like the group membership is not updated while user is logged in. I tried to lock and unlock the session. I’ve tried to put the pc to sleep. I’ve tried hibernate. None of these changed anything. I also left the pc running over night, hoping time would help. It didn’t.
Is there really no way to update the effective group membership while a user is logged in?
(In windows group membership of a running session will update when the pc is locked/unlocked)

Log out and back in.

That’s basically the same as a reboot on a laptop - anything open has to be closed. I’m hoping for a way to do this while keeping the session running.

$  su - username 
$ thunar directory &

Try that.

Thats a sort of workaround, yes. But it also means any software has to be started from terminal. Knowing myself, the lack of this functionality will end up making me lower the system security because I will permanently run with privileges I need only a few times a year. I don’t like ending my session. There really should be a way to reload config in xfce, like can be done with (most?) server services.

How often do you need to add new groups to users??

Sounds like you need to do it multiple times a day. Although I can’t see what usecase that would require that.

If we say 10 times a year. Then I end up having to reboot the linux laptop more often than the windows laptop!

If you’re planning on rebooting only 10 times a year - you’re on the wrong distro (type).
Rolling distros tend to get updates - and updates of kernel, desktop environment, systemd or core libraries will need a reboot to work properly.

If I do the updates those days when reboot is acceptable, that shouldn’t be a problem