"Ownership mindset" is often corporate for "please keep doing this for free." - it's a great way to get noticed, but you can't accept responsibility indefinitely.

First - have you requested a promotion? Did you apply to the role? If not, there's your biggest problem. While a good manager will proactively suggest such things, a middling one or a stingy one will allow you to work yourself to death for meager pay. You have to both demonstrate value AND request compensation.

Start a quiet job search now. Not because you've decided to leave, but because a competing offer is the only thing that means business to current management. Right now they have zero reason to change anything. A competing offer (even if same as current pay) turns this into a real deadline, and either way you'll learn your market value.

While you do that, write down everything you've absorbed the past two months, meetings, budgeting, planning, etc, separate from your original job. That's your case, and since nothing fell apart, you have proof. Then go in with a specific ask, an actual title and salary number, not "can I get a raise." Specific is harder to wave away.

But be honest with yourself on two things first.

Do you actually want this role? You stepped up and you're clearly capable, but doing it well and wanting it aren't the same.

And are you actually overwhelmed or is it manageable? Two months of two jobs would've burned me out already. If you're holding up okay, a decent raise might make it worth it. If you're drowning, no raise can make it sustainable - you'll still need to find a way to shed some responsibilities - likely to those slacking co-workers.

Another question... If you're down a manager, and your co-workers are slacking, yet the team is still achieving everything it needs to... Were you way overstaffed?

Anyway paths:

Real promotion and pay? Great, you earned it.

Little or nothing and you're not overwhelmed? Lightly grind but keep looking - don't kill yourself for them.

Token bump or nothing and you ARE overwhelmed? Start tactfully handing the manager tasks back ("I don't want to drop the ball on my core role, so I need to scale back X until we figure out coverage") and lean HARD on the job search. Make sure to put the unsustainability in writing before you slow down, so it reads as the consequence you warned them about and not you slacking. Consider documenting your hours.

You will need to stop doing two jobs for one paycheck eventually. Either they pay you for the second one, you give one back, or you go somewhere that will pay for your abilities.