In the settings, gadgets are not shown. We are facing difficulty in adding reference, category etc. without the gadgets. Can anyone look into the matter?

Yes, it is Asia/Kolkata.

In T321246#8497769, @Urbanecm wrote:

The wiki is live, but I had to ignore the timezone, as it has to be provided in a format recognized by PHP (ie. one of the timezones listed at https://www.php.net/timezones, see https://www.mediawiki.org/wiki/Manual:$wgLocaltimezone for details). Once it is clarified, I'm happy to fix the wiki configuration.

I also intentionally ignored "Local file uploads: enabled", as that requires an Exemption Doctrine Policy (EDP) to be in place (see Licensing policy WMF Board resolution), which doesn't seem to be provided.