If your champ doesn't deal %max-HP damage or true damage in any way, I would just continue to build damage and target the enemy squishy. If their tank is on top of you and you can't dish out any damage without dying then get some defenses. Rely on your allies who do deal maxhp / true damage to deal with the Tank.

Liandrys, void staff, morellos, raileis if you cant escape, warmogs, boots, something else

Best you can do it poke over time, try not to engage, stay alive, and hope your team isnt going to engage too early

Unless they're all tanks, just focus on the squishies and keep space from the tanks. Not every champ can melt tanks, rely on your teammates who can. If no one can take down tanks then just ff and go next, sometimes you just get a bad comp that's just the nature of ARAM

Lots of good suggestions here. I personally like building BotRK, sometimes even on champions it normally doesn't make sense on (like tanks). The percentage damage is incredibly useful, and it doesn't always make sense to build AP %-burn items.

The only thing that works a bit is getting fed before they do. As a tank enjoyer, it’s difficult to bounce back if you get screwed early

As a mage stack cdr and build items with health, tanks won't be able to kill you and you'll be able to spam your CC (and damage). Third or fourth item you can build a Warmogs and then you'll be able to heal up after an engagement.

Mages are generally pretty bad into tanks, and that's a significant reason why they tend to be weak in ARAM (unless they have great range or are named Brand or Swain). Most of the time you can have viable options to help like Liandry's, Void Staff, and Rylai's as others have mentioned. But honestly it might be best to try to reroll into something else. Usually ARAM teams have too much magic damage, and that makes it easy to itemize against.

I remember seeing a discussion over a premade ARAM team with hundreds of games and 99% winrate. They would roll for a comp with 3 melee frontliners, 1 ADC and 1 mage/enchanter. Sometimes the rolls don't work out like that, but I would try to pick from rolls to fill in those gaps if you want to win. Or just play someone who seems fun, that's good too.

Zwiiww

Divine sunderer bruiser build tbh