Opera was useful to me at three very specific points in time for very specific reasons:

When I built my first PC out of old scrap parts in the early 2000s, the only halfway modern browser that was still compatible with Windows 95 and a 486 CPU was Opera. Not the latest version, but new enough to be usable. This version, which came with a permanent toolbar urging users to purchase a full license, already had tabs.

I did not have broadband Internet until 2006. Even 56k modems didn't work with the awful telephone line we had - I had to make do with 48k. The proxy service with compression Opera came with was the only way to browse then current websites without waiting for half an hour for a page to load.

When I bought my first touchscreen phone in early 2009, the LG KP500, a Java-based phone with only 2G and no WiFi that pretended it was a smartphone, Opera Mini was the only browser that was usable, again thanks to its proxy service.

Outside of these niche use cases, I never saw a reason to use Opera instead of Firefox. While it was an important innovator in the beginning, for me personally at least, it has always been nothing but an "emergency" browser and ever since it was bought out by a Chinese firm and switched over to Chromium, there was no reason left to use it other than brand attachment.