This is an incredibly dumb requirement, if intentional. No other portal has such a requirement, not even the other 2 portals currently up that go to the same continent.
And before you ask, no, I don’t have any alts that have done BFA. I started in late DF.
None of my 80s can use the portal - Horde and Alliance included.
Can confirm, I went on my main from BFA, zero issues taking the portal (as horde even).
I tried on like 6 different toons that have completed the bfa campaigns multiple times. still unable to use it aswell.
It’s still not working today even after their update this morning. Hopefully it will be fixed.
I just took my lvl 51 worgen druid to COT and was able to use the portal. This toon didnt do anything except farm for the bee mount. so its nothing to do with campaign ?
** only suggestion i can offer would be take a trial toon or a lowbie alliance toon down there to use the portal for the achievement**
Given the UI, reputation and lag issues still exist, I wouldn’t hold my breath.
Got it to work on my Kul Tiran 80 but no one else
Same here.
Tried accessing with 2 lvl 80 Horde (1 that played BFA, 1 that didn’t) and portal no workie,
Had success with the portal on a Mists Remix created Kul Tiran druid that had only stepped foot previously in BFA zones for the Heritage Armor stuff.
I have completed the intro quests for BFA as horde, and the portal did not work. I have completed the expansion on my ally toon, and was able to use the portal. For those without coords, it drops you where the Title of Tradewinds Market, on the word MARKET, the K upstroke to the right, between the K and the E. Happy hunting all, and feel bad for all of us who are trying (and qutie a few failing) to get this one.
Fortunately, it is possible to get the achievement missing this portal. The achievements with missing tic marks will just forever be a reminder of the low quality standards introduced with this expansion.
BfA quest progression status didn’t matter for me; neither my main nor alts can use the Tiragarde portal in Tanaris.
Just spent the last 12 hours finishing every BFA story quest I could. I only played for the first half of release. I did 3 raid questlines, all war campaign, and extra heart of azeroth quests. Still can’t get in portal. Looks like you need a very specific quest done and we need blizzard to expand on it
Still not working
ty for this I will do it that way.
Unable to use portal as well
The workaround didn’t work either. It didn’t tic the name anyway.
Found the portal in Tiragard and went through it. So the return works on Horde.
It’s just the portal from the Anniversary grounds. Yes I do have BFA.
Following the tip here, I tried with my only Alliance toon below Level 80 (Worgen Rogue, Level 77), and I was able to use the portal. None of my other 7 toons could use it, including my one Horde toon below Level 80.
X 13 Horde
X 2 Alliance
None of them could enter the portal
The portal switched over to Shadowlands zones this morning. 
Thanks to all for reporting your findings. I was able to use the portal on a level alliance 80 mage that I played in BFA, but hopefully it will be fixed for everyone before coming back around again.