For working with a large set of hosts to monitor I need some way to search for the hosts I am interested in, e.g. all hosts on a proxy p1 and manually assigned template xyz that are not in host group abc. Something like that.

I cannot speak for Zabbix 4.2, but in Zabbix 4.0 searching for the hosts to work with appears to be very limited. Very often I have to use ^F in the browser to search for the items I am interested in. This could be improved.