Is it possible to have calls specifically aimed at women and under-represented groups in a specific thematic area?

It is possible but it needs to be well justified in the proposal so that evaluators see the pertinence/ relevance/ added value of the proposed programme. There have been a few programmes focusing at specific target groups in the past. Examples:

Rosalind Franklin Fellowship Cofund Programme

REinforcingWomen In Research

VINNMER-PEOPLE