Back in February, a new version of Chrome changed the way that users activate a custom search engine in the Omnibox: instead of indicating the engine and beginning your search string with a tap of the space bar, you had to press tab instead. Long story short, everybody hated it, so Google reverted the change and tried something else. Well, the tab-to-search functionality is back ... but don't worry, it's buried deep in Chrome's Flags menu.
Starting with version 92.0.4503.0, Chrome Canary offers a new option in chrome://flags/#omnibox-keyword-space-triggering-setting. It's disabled by default, so enable the flag and reboot the browser if you want to check it out. Then head to the main Settings menu, click "Search engine" on the left column, and then the "Manage search engines" entry.
At the top of the familiar search engine listing, you'll see a new option allowing you to choose between hitting the space bar or the tab key, or manually switching it to the tab key only, as was the case back in February.
Response to the switch to tab activation seemed almost universally negative, since custom Omnibox search engines are a pretty big deal for Chrome users. So we couldn't guess why Google is bringing it back after reverting the change, even in this rather roundabout way. The previous choice of using double space to activate the search keyword seems to have fallen out of favor for some reason. As with all changes made to the Canary build, it's anyone's guess as to whether this will come to beta or stable, or be kicked out of Chrome after even more user testing.