Hmm, there is a setting that controls whether it appears on that menu. I'm not sure why yours is hidden, but you can try toggling the setting manually:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste browser.tabs.unloadTabInContextMenu and pause while the list is filtered

(3) Double-click the preference (or click the toggle button at the right end of the row) to switch the value between false and true

Any improvement?

Filtering the results indicated a true setting. I toggled it twice to get back to true and then explored the tab options again. Still no unload option.

Neither the automatic nor the manual unloading feature is available for use despite my having the latest version.

Hello

https://support.mozilla.org/en-US/questions/1536369