@leocg Good to know that. I just tried it out and I am again into same problem (which was resolved after uninstalling & re-installing Opera). I think this feature might not be stable yet for MacOS Big Sur (This OS does not seem to be straightforward compatible with things in market)

@leocg yes, I had tried uninstalling the "Chrome extension installer" extension with no luck.
later, I tried uninstalling entire Opera and now it works fine.

Thanks @karbonat for taking time to respond to my question.

I uninstalled the Opera and re-installed and re-setup everything .
Now, I am able to install the Chrome Extensions.

@karbonat Yes, I have that extension on Opera. But, something went wrong after I upgraded Mac to Big Sur.

No more able to install any Chrome extensions in Opera. This was the main reason I was able to migrate to Opera easily. But, now that reason itself is gone.

There are tricks to download and manually push the extension. But, I am interested in installing 1password which is paid extension, so it does not allow trick.