Linking to X, formerly, known as Twitter has been made troublesome as the software that runs these forums does not accept x.com as a source. The software accepts twitter.com but not x.com. I reported this issue over a month ago and, as usual, the request was ignored. Hopefully, someone will add x.com to the list of accepted media sites, someday. Until then, if you wish to post a tweet here the easiest way is to use the Media icon, , and enter the URL supplied by X and click on Embed. This will fail but will also display the URL at the beginning. You can then replace the x with twitter and then click on Embed.
Fun fact, the twitter domain still works. So if you change x.com to twitter.com, it should work as expected.
I don't ever have trouble posting Twitter/X links. I just copy the link and embed via the media (looks like film). If anyone does, let us know.
I just open the X link in a browser and then copy the Twitter link that it redirects to. One more step, but simple.