@cubmanky, what Zen Cart version did you upgrade from?
Yep, you're running into the same upgrade-related issue that I identified in this (https://github.com/zencart/zencart/issues/5932) now closed Zen Cart GitHub issue.
You're upgrading from 157c to a 158 (or later) version and you have a 'core' language-file override that uses the now-legacy format: /includes/languages/english/bootstrap/header.php. Unfortunately, at this time, you'll need to manually make the change to that/those language files to convert them from using PHP define statements to using the now-required array format.
So in Admin >Tools> layout boxes I have the bootstrap header search turned on but I do not see any box until I turn the normal search on. Any suggestions?
Is there anything logged in your LOGS directory?
Also, I doubt this would make a difference, but make sure that your "sideboxes/bootstrap/search_header.php" has a unique Sort Order variable, just in case there's some weird conflict there.
I did a test and turned off my "sideboxes/bootstrap/search.php" but I am still able to see my "sideboxes/bootstrap/search_header.php" load just fine.
- Jeff
I would like to add the language selection and other links to the burger menu (three horizontal lines on top left) of the mobile display. If I configure tpl_offcanvas_menu.php, the changes are displayed in mobile and desktop display. How can I add links, etc exclusively to the menu of the mobile display?
Ahhh, it is a Bootstrap thing and not controlled by files in Zen Cart. Add class="d-lg-none" to the links in the menu, so they do not show up at bigger displays. More here: https://getbootstrap.com/docs/4.0/utilities/display/