new day, new try, new error 
(changed to python3, → replay notify via webgui → notifications)
> Traceback (most recent call last): -- File "/omd/sites/azure/local/share/check_mk/notifications/msteams", line 10, in <module> -- context = dict([ (var[7:], value.decode("utf-8")) -- File "/omd/sites/azure/local/share/check_mk/notifications/msteams", line 10, in <listcomp> -- context = dict([ (var[7:], value.decode("utf-8")) -- AttributeError: 'str' object has no attribute 'decode'
notify.log
46 2022-04-27 09:20:58,710 [20] [cmk.base.notify] ----------------------------------------------------------------------
47 2022-04-27 09:20:58,710 [20] [cmk.base.notify] Analysing notification (XXX-PKR) context with 36 variables
48 2022-04-27 09:20:58,711 [20] [cmk.base.notify] Global rule ''...
49 2022-04-27 09:20:58,711 [20] [cmk.base.notify] -> matches!
50 2022-04-27 09:20:58,711 [20] [cmk.base.notify] - adding notification of monitoring via msteams
51 2022-04-27 09:20:58,712 [15] [cmk.base.notify] Global rule 'Notify all contacts of a host/service via HTML email'...
52 2022-04-27 09:20:58,712 [15] [cmk.base.notify] -> does not match: The host's name 'XXX-PKR' is on the list of excluded hosts
53 2022-04-27 09:20:58,712 [15] [cmk.base.notify] Global rule 'Only one notify during a service problem'...
54 2022-04-27 09:20:58,712 [15] [cmk.base.notify] -> does not match: This rule requires membership in a service group, but this is a host notification
55 2022-04-27 09:20:58,713 [20] [cmk.base.notify] Executing 1 notifications:
56 2022-04-27 09:20:58,713 [20] [cmk.base.notify] * would notify monitoring via msteams, parameters: url_prefix, webhook, bulk: no