Hello everyone. I'm new around here and I'm immediately bugging you with questions, I know.

I'll try to make this post as informative as possible.
I ended up in charge of a web shop that uses the following:
Joomla! 3.8.7 Stable
VirtueMart 3.2.4
Template: TP Runway (I think)
Overrides: not sure if there are any, where to check?
PHP Version 7.0.33
Database Version 5.5.5-10.1.38-MariaDB
Using SEF links: YES
The problem that I have is that the "Add to Cart" button doesn't work in category view, but it does when I open up product details page. I know that there has been dozens of topics about this problem already and I
narrowed down the issue to the fact that category view layout declares
jquery library twice, at least I think that's the issue.
As you can tell I'm not really a Joomla guy, and I'm even less of a Virtuemart guy. Sorry about that, I'm still learning.
Check this out:
https://www.masiva-bj.hr/index.php/rezervni-dijelovi-za-traktore/ursus-330-335/motor-19/results,64-84.html
When you click the "Add to Cart" button here, in Firebug console window the following error is recorded:
TypeError: jQuery.fancybox is undefined
However here:
https://www.masiva-bj.hr/index.php/rezervni-dijelovi-za-traktore/ursus-330-335/motor-19/0305016-detail.html
Adding to cart is working just fine.
Note, I didn't include live links because I wasn't sure if I'll be able to post this message then or if it's against the rules.
I checked the source page of both Category View and Product Details view and by reading previous topics on this issue I discovered that possible cause of the problem is that Category View has jquery from Google declared additionally, next to the ones from Joomla/Virtuemart themselves. It's on line 1169:
1169: <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
What I tried to fix this issue is the following:
Activating/deactivating various options in Virtuemart >> Configuration >> Templates >> Activate Css Styles & Javascripts but nothing helped.
Disabling various modules/extensions that I noticed are from Google, like BT Google Maps, Google Analytics, no go, didn't help.
I tried searching in templates where this additional jquery from Google is declared, but I couldn't find anywhere and I got lost in the category views/layouts/sublayouts.
What I need is a little push in the right direction where I could find this additional jquery that's declared.
Where should I start looking? How can I find out if it's a module including this additional jquery, or is it hardcoded somewhere in actual files?
Maybe I need to purge cached website HTML pages, you know static generated HTML files which this website does use?
Any input is greatly appreciated, cause I think I'm really close to cracking this one.
Thank you in advance.
Zoran.