What is the ERC (European Research Council)? Find more information here:

-ERC website
-Euresearch: the Swiss guide to European research & innovation

Q: Can a panel member, who is evaluating for instance ERC StG apply for another type of ERC grant (CoG, AdG, SyG) the same year she is panel member?

Yes, a member of the ERC StG panel can apply for an ERC AdG in the same year. What he/she cannot do is apply for the same type of grant where he/she is a panel member.

In the 2020 ERC Work Programme, page 20, you can see the following:

A Principal Investigator who is a serving Panel Member for a 2020 ERC call or who served as a Panel Member for a 2018 ERC call may not apply to a 2020 ERC call for the same type of grant.