This is just an extra information injected in PeerTube HTML that is required by Twitter/X. If you don't have a Twitter/X account, just leave the default value.
<x id="START_TAG_STRONG" ctype="x-strong" equiv-text="I al"/>I already have an account<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/>, I log in