Maybe between SLES 15.3 (where this document is based on) and 15.5/15.6 the package promtail was changed/enhanced?
At least there is no "loki" user account, therefore the usermod command won't work. (-> if you are using SAP logs like the HANA traces, do not forget to add the loki user to the sapsys group: usermod -G sapsys -a loki)
Documentation needs to be adjusted....
Output of a 15.6 box:
# lsof | grep promtail
promtail 4314 4325 promtail root 14r REG 0,24 8388608 75 /run/log/journal/8936aef07eda4a649528353ff8f131b6/system.journal
So here promtail is running under root rights, which is also not perfect....