Google Assistant Summarizer is only in US. But you can try using Gemini instead. A few leagues better than Google Assistant Summarizer.
Just activate Gemini and there will be a button to link the URL (can be use for image, screenshot, YouTube video) then ask Gemini to summarize it or type in a summarizing prompt (i usually pinned it in my clipboard). If you want to ask more stuff relating to the topic, can press the mic button to ask more or simply just jump into Gemini Live. Gemini will remember the context of the conversation from the moment you activate it. Pretty insane, tried for YouTube video in Chinese and it works too.
It used to be able to work for websites with pay wall but a few months back, it doesn't work and it will simply just take a screenshot.