Hi, in short words, custom work. Because by default the WordPress navigation functions loop through all the items AND a portfolio item may belong to multiple categories.

Hi there,

we have a minimal fee of 50 Eu because we are very tight with time. And the job is within 1 hr (or rate is 50 Eu / hr)

Basically you need to modify /sections/project_navigation_section.php and setup the next_post_link and prev_post_link to work within the same category

https://developer.wordpress.org/reference/functions/next_post_link/

then you need to modify /include/hooks-config.php so that when you reverse to the first item it has to be the first item within the same category.

https://prnt.sc/J9UuC_XCX2Z3

OK, closing this for now