No, it is not permanent. It looks the drop in traffic is because of competition. Competitor's analysis is recommended. This will lead to where and what should be improved...

Please provide the URL.

I checked all the names are in Capital letters only.. what can I do?

Check anchor text also where you might have used your site name in small letters.

Use hreflang attribute to avoid the duplicate content issue. More information is here, https://www.semrush.com/blog/hreflang-attribute-101/

Are you saying to check the home page meta title is correct or not.. Am I right? but I didn't include the website name in the meta title?

learningseo.io is also a great resource!

If they are gone on purpose, you should not do anything about it. It is supposed to 404, when the content does not exist. If you get more products in the future, then it...

Check title tag on your site, using Inspect tool. Does it match the snippet?

If you have rel=canonical fixed already and it didn't help, I'd try to remove those duplicate pages from sitemap. Also check, if there isn't canonical self-reference on t...