Hi, I need help with the following problem.

I am using tatiana theme. A few days ago the page was working perfectly, but today I tried to make a new publication. The "Add new listing" page opens correctly. I fill all the fields until the end, but when I click the "publish" button nothing happens.
The same thing happens when I try to edit an item. The "Edit listing" page open with all the information. When I make the pertinent changes, I hit the "save" button and nothing happens either

Check browser console for javascript errors.

The problem came when I switched from JQuery Version 1.x.x to 3.x.x.  In JQuery Ver 1.x.x it works perfectly, but I have a problem when using JQuery 1.x.x the Tatiana popup (fancybox) shows very small and not visible right.

This theme may not work OK with JavaScript 3.x, even it was updated to provide at least bit of compatibility.

 What do you recommend me to do, using JQ 1.x.x to solve the problem of popup (fancybox) that shows only a very small picture and is not visible right?

Maybe to check what fancybox library version is used, try to replace with older or review theme JS if size is defined here.

Fancybox library version used is: 2.0.4

How to replace Fancybox Ver. 2.0.4.
How to define the size in JS?

Really, I am a newbie in this field. I want to start a new classifieds business. Of all the themes, Tatiana is the one I like the most, but it is not working correctly, as I have explained to you before. I know that this is a free theme, but if I have to pay for it, like the others, I'm willing to do it. I really need your help in this matter. Thanks

Hello, can someone help me with this matter? I have tried to solve the problem with the instructions you gave me, but I have not been able to solve it. Also, I tried the demo that is online and it doesn't work correctly either. It seems to me that the problem is in the theme itself.

Yes thats possible, thene was made on jQuery 1.x including all libraries.

This theme is old and many people have used it in the past. It is assumed that previously, the theme was working perfectly with jQuery 1.x and now the fancybox doesn't want to work as it should. What can be done to correct this small problem?

Spent a little money and buy a new theme

Not sure, checked demo and it works OK there.
https://tatiana.mb-themes.com/for-sale/cell-phones-accessories/mercedes-tourer-2014_i60

You can theoretically use older osclass version with older script versions.