In new Zabbix we can connect trigger/events to IT services by tag.

doc (Problem tags):

https://www.zabbix.com/documentation/6.0/manual/web_interface/frontend_sections/monitoring/it_services#service_configuration

It will be good to have another option "by severity" (AND severity IN '...')

Why?:

Because we can define the same tag for many triggers, but for "business" purposes we can be interested only with triggers with severity "disaster" (or "high and above" or "average and high and above" and similiar...).

Also because in Zabbix 5.0 (and lower) we can connect one trigger to one IT service. And this trigger have one strict severity. But like above trigger can have tag that is "shared" between other triggers.