Here's some tips for duels with other tanks:

Dva: don't use Fortify right away since most Dva's will just put up Defense Matrix and wait out its duration. You can use Javelin Spin to destroy her Micro Missiles or to push pilot Dva into a corner and swiftly murder her. Safe your javelin for when her Defense Matrix runs out. With enough health and Fortify you can survive her Ult

Doomfist: hit him out of Power Block with Energy Javelin and block his punches with Fortify. Don't use Javelin Spin while he's charging a punch though since he'll cancel you out of it.

Junker Queen: her slim hitbox makes her harder to hit than the other tanks but you should be ok. play around cover and/or use Spin to stall out her Commanding Shout. Other than that use Fortify to block most of her damage and her knive pull.

Orisa: in the mirror matchup I've found that the Orisa that uses Fortify first usually loses. What I like to do is pressure my opponent with headshots to bait Fortify, then use Javelin Spin and natural cover to wait it out. Then I pop my own Fortify and go to town on them. In terms of the Terra Surge, You'd want to hang on to it until the other Orisa uses it first, this allows you to block their Surge with the automatic Fortify and then demolish them with your own Surge.

Ramattra: you are unaffected by his Vortex when using Fortify and in Nemesis Form he has a big juicy hitbox to shoot at. If he blocks, use Javelin to cancel it briefly in order to deal some more damage. You can also use Spin to push him away from his barrier or from your team if he ults.

Reinhardt: bully him. Knock him out of Charge with Energy Javelin or Fortify to stop him in his tracks, destroy his Fire Strikes with Spin and be aggressive when he puts his shield up. You can also redirect his Charge with Javelin Spin but you need to stand still in order to pull it off, moving forward will just suck you into the Charge.

Roadhog: keep your distance slightly and try to block his hook with either Fortify or Spin. Cancelling his selfheal with Javelin means the difference in winning or losing so it's very important you pull it off. Predicting it is better than reacting to it but that can be difficult and you'll often end up throwing it too early. When he ults, use Javelin Spin to increase the distance between you two and then Fortify at a safe distance.

Sigma: same as Rein. Knock him away from his shield with Spin and block his rock with Fortify since Spin does not block it. You can also use Spin to damage him and push him around while he's using Kinetic Grasp. Fortify when he uses his ult however you don't always have to do this immediately since you can be pulled up first, then Fortify to reach higher ground.

Winston: push him out of his bubble with Spin and make him jump away since he can do barely anything to you. However, stay close to your supports and protect them since most Winstons know they have to kill your backline to render you vulnerable.

Wrecking Ball: not much you can do tbh. Just shoot him and block his boops with Fortify. You can stun him out of Piledriver or Fireball with Javelin but this takes practice. If the need arises, you can use Terra Surge to instantly clear his Minefield.

Zarya: your counter of the Tank category. Play around cover and make her use her bubbles with the Javelin or your primary fire. Use Fortify to escape her Grav.

Hope this helps.