back to mainpage fails by clicking on the logo

when I click on a linked site (e.g. about me in the navigation bar) and want to return to the main theme page by clicking on the logo, a new window opens infront of the about page?

do your have any clues how i can solve the issue?

please visit

https://www.schlachtensee-fotograf.de

then click on “über mich” and afterward please return to the main page by clicking at the logo

thank you very much in advance