Chrome extension popup not showing anymore

If changing it from "page_action" to "browser_action" still does not work, check to see if your manifest defined any background.js and if that background.js has set any rules.

For example:

In the case of the Getting Started example from Google, the background.js had an onPageChanged rule where the url host must be 'developer.chrome.com' for the extension to be active.

replace

chrome.declarativeContent.onPageChanged.removeRules(undefined, function () {
    chrome.declarativeContent.onPageChanged.addRules([{
        conditions: [new chrome.declarativeContent.PageStateMatcher({
            pageUrl: { hostEquals: 'developer.chrome.com' },
        })
        ],
        actions: [new chrome.declarativeContent.ShowPageAction()]
    }]);
});

with

new chrome.declarativeContent.ShowPageAction()

so that the extension popup will be active for any page.

(This took me ages to figure out, so hope it'll help others)

In manifest.json replace "page_action" (which only works on specific pages) with "browser_action" (which works on all of them).