Short: Found the error. Update changed behaviour, what worked before was broken now. Fixed it.
Long story:
Before:
- type: conditional
conditions:
- entity: sensor.dwd_wetterwarnung_current_warning_level
state_not: '0'
card:
type: entities
entities:
- type: custom:multiple-entity-row
entity: sensor.dwd_wetterwarnung_current_warning_level
name: WARNUNG
toggle: false
state_color: true
show_state: true
secondary_info: ''
icon: mdi:exclamation-thick
entities:
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_name
name: Warnung vor
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_start
format: time
name: Von
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_end
format: time
name: Bis
state_header: Anzahl Warnungen
column: true
card_mod:
style:
.: |
ha-card {
margin-left: -15px;
margin-right: -15px;
margin-top: -15px;
margin-bottom: -15px;
box-shadow: none;
}
:host {
--paper-item-icon-color: red;
--mdc-icon-size: 40px;
}
After/Now - working again (icon is RED):
- type: conditional
conditions:
- entity: sensor.dwd_wetterwarnung_current_warning_level
state_not: '0'
card:
type: entities
entities:
- type: custom:multiple-entity-row
entity: sensor.dwd_wetterwarnung_current_warning_level
name: WARNUNG
toggle: false
state_color: true
show_state: true
secondary_info: ''
icon: mdi:exclamation-thick
entities:
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_name
name: Warnung vor
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_start
format: time
name: Von
- entity: sensor.dwd_wetterwarnung_current_warning_level
attribute: warning_1_end
format: time
name: Bis
state_header: Anzahl Warnungen
column: true
card_mod:
style:
.: |
:host {
--paper-item-icon-color: red;
--mdc-icon-size: 40px;
}
card_mod:
style:
.: |
ha-card {
margin-left: -15px;
margin-right: -15px;
margin-top: -15px;
margin-bottom: -15px;
box-shadow: none;
}
So while --mdc-icon-size was still applied to the icon when targeting on the entities card, --paper-item-icon-color now only is working when being applied directly to the custom:multiple-entity-row card.

I´m good now.