How can I check whether my X account is shadowbanned?

Type your handle without the @ and run a scan. X Shadow Ban measures four things: search suggestions, posts in search results, hidden replies in a public thread, and reply ranking. Each result is labelled pass, fail, untestable or error with its own confidence and limitation.

Then verify manually: log out or use a private window, search from:yourhandle, type your handle into the search box to see autocomplete, and open a public thread where you replied. A difference between what you see logged in and logged out is the signal a checker is trying to detect.