found it.
Line 335 in functions.php.
Was:
'footer' => sprintf( __( '%1$s %2$s %3$s . ', 'museum-core' ), '?', date('Y'), get_bloginfo('title') ) . sprintf( __( 'Museum Core by %1$sMuseum Themes%2$s is proudly powered by %4$sWordPress%2$s.', 'museum-core' ), '<a href="https://museumthemes.com/" target="_blank" title="Museum Themes">', '</a>', '<a href="https://www.remarpro.com" target="_blank">' ),
Should be:
'footer' => sprintf( __( '%1$s %2$s %3$s . ', 'museum-core' ), '?', date('Y'), get_bloginfo('title') ) . sprintf( __( 'Museum Core by %1$sMuseum Themes%2$s is proudly powered by %3$sWordPress%2$s.', 'museum-core' ), '<a href="https://museumthemes.com/" target="_blank" title="Museum Themes">', '</a>', '<a href="https://www.remarpro.com" target="_blank">' ),