Bookmarklet to search a user's X timeline for a specified "term". Navigate to the user's profile page (x.com/user) and then click this bookmarklet. A pop-up window appears, asking for your search term. Returns the native X search results page, prepopulated with that term and limited to that user.

Xterm.js

//bookmarklet by redditor @chickenandliver - https://www.reddit.com/r/bookmarklets/comments/1f7wk72/search_a_users_x_timeline_for_term/
javascript:(function(){
    const term = prompt('Term?');
    if (term) {
        const username = new URL(location.href).pathname.split("/")[1];
        window.location.href = `https://x.com/search?q=${encodeURIComponent(term)}%20(from%3A${encodeURIComponent(username)})&src=typed_query&f=live`;
    }
})();

//Minified version -
//javascript:(function(){const term=prompt('Term?');if(term){const username=new URL(location.href).pathname.split("/")[1];window.location.href=`https://x.com/search?q=${encodeURIComponent(term)}%20(from%3A${encodeURIComponent(username)})&src=typed_query&f=live`;}})();