None of the suggestions above works for me.
sudo snap-store --quit-on-close-for-update
[sudo] password for wim:
mkdir: cannot create directory ‘/run/user/0’: Permission denied
Warning: Schema “org.gnome.system.locale” has path “/system/locale/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
Warning: Schema “org.gnome.system.proxy” has path “/system/proxy/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
Warning: Schema “org.gnome.system.proxy.http” has path “/system/proxy/http/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
Warning: Schema “org.gnome.system.proxy.https” has path “/system/proxy/https/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
Warning: Schema “org.gnome.system.proxy.ftp” has path “/system/proxy/ftp/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
Warning: Schema “org.gnome.system.proxy.socks” has path “/system/proxy/socks/”. Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
13:17:26:0326 GLib-GIO g_app_info_get_name: assertion ‘G_IS_APP_INFO (appinfo)’ failed
Unknown option --quit-on-close-for-update
wim@wim-System-Product-Name:~$ sudo snap refresh snap-store
error: cannot refresh “snap-store”: snap “snap-store” has running apps
(ubuntu-software), pids: 2288
wim@wim-System-Product-Name:~$ sudo snap refresh snap-store
error: cannot refresh “snap-store”: snap “snap-store” has running apps
(ubuntu-software), pids: 2288