I am having the same issue.  I gave up trying to use Intuit Link last year with Lacerte but thought I would try again for 2020 tax filings.  I tried sending the Link Organizer out of the 2019 program.

I sent to my husband's email when I clicked on the Sign In from the email it opens in Microsoft Edge where there are no bookmarks or any cache history for the website as he doesn't use it,  The link in the email the takes me to as screen that says this.  I tried  re-inviting and it still gives me this.  I tried signing out and signing in with the email address I sent the invite to and still no luck.

I'd really like to use this but if I can't figure it out I can't explain it to my clients, some of which are older but are willing to try using this.  Any suggestions as to what I'm doing wrong?