seriouslly dirty workaround (probably not appriciated by the linux admin):
mkdir -p /grafana
mkdir -p /grafana/redirect
sudo mount -r --bind /home/pi/redirect/sqlite3 /grafana/redirect
define data source as /grafana/redirect/redirect.db → works
fstab entry:
/home/pi/redirect/sqlite3 /grafana/redirect none bind 0 0
does the plugin and / or grafana has a problem with anything in /home?