UPDATE July 2023: I did some testing (as you could have guessed :D). 83 requests at launch to various Opera and Google domains. There is nothing like Firefox Glean that monitors your entire browser activity, so at least it seems you can change settings, etc in peace. But, Opera has a spyware feature that is probably the most violating in existence, namely that it sends every website you visit to itself (through the request sitecheck.opera.com), collecting your entire browsing history (fortunately, you can disable this). Even though Opera has recently whined about being called a spyware, nothing has changed; the amount of unsolicited requests at launch is even exactly the same as all those years ago.
This browser has a lot of features, and has included many new ones since I last tested it. Integration with spyware platforms like WhatsApp and Telegram is still there, but also ChatGPT as a recent addition. A "VPN" that is probably a Chinese honeypot since Opera is now owned by a Chinese company. Automatic currency conversion, built-in adblocking (but not enabled by default; the acceptable ads list is automatically downloaded from Adblock Plus and reports your browser). Wallpapers, cryptocurrency integration (I'd be wary of using this, but didn't test in depth), IPFS, many many more things I didn't even look at; even has weather reporting in its new tab page which of course sends your location. And a bunch of ads (these are location-aware):
By default, it does the same crap as Google Chrome in sending every letter you type to its search engine live. But it's modifiable and you don't even have to use Google as the search engine - though the defaults are disgusting, and they matter. I don't really like this browser; it's really heavy spyware and isn't even open source - but does contain many many features not found elsewhere that will surely appeal to some. Uses 260 mb RAM with one empty tab; requires GTK3 like all Chrome-based browsers. Hey, WebRTC can be nicely disabled from the settings menu, which is a positive, I guess; but again, the default sucks. In the end, you have to stack the features against the spyware and the lack of source code; for me, Opera is still in a losing position since extensions can replace many of the features, while the spyware remains. Hey, I even tried to disable all the spyware just to be charitable, but it's not possible. There are still auto-update requests at every Opera launch, requests to Google for some updates, requests to download the location-aware ads with a unique ID attached, and even a TCP request to mtalk.google.com. Sorry, but your features are not enough to save you from being a violator.