It might be useful to say where you got the instructions from – people then might have a better chance of assisting you with any problems – and also to state exactly what you observed/what went wrong (rather than "I failed to adapt these commands").
I posted one version of these in an answer on Android StackExchange, here:
https://android.stackexchange.com/questions/56635/how-can-i-export-the-list-of-open-chrome-tabs/199496#199496.
Those commands do work for me with Vivaldi for Android version 6.5.3217.103. However, it's always possible that Vivaldi, or any other chromium-based browser, might disable or remove this method of debugging in the future (Brave has considered doing so).
As mentioned in my StackExchange answer, you can check what Unix domain sockets exist on your phone by running adb shell cat /proc/net/unix. If your browser is running, but a socket named @chrome_devtools_remote isn't in the list, then your browser simply doesn't support this method of debugging. (I'm not sure what happens if you have multiple chromium-based browsers open on your phone at once – do they all try listening and writing to the same socket? Perhaps so.)
Another possibility is that curl might initially output an empty JSON list ([]). Occasionally I've had that happen, but it seems to be an intermittent error, and waiting a few seconds and trying again has retrieved the full list of tabs.
