Both have handed in resignations even before testing, but are still working for the team?

Why not? It's not like they could learn any valuable secrets that could help the competition.

So are they still running Alfa equipment until Audi takes over?

There is no Alfa Romeo equipment and there hasn't been in decades. You got fooled by a mere branding deal with Sauber.

Even worse than Racing Bulls.

Seems like Racing Bulls isn't a thing:

I like Alfa as a car manufacturer, sad to see them leave.

So sad to see the Alfa Romeo PR department leave. They contributed so much...

I guess with war criminals Aramco and Petronas being title sponsors for other teams, it could have been worse.

It's not but the rules say nothing against occasional posts about other forms of motor racing either.

Yep that’s all they do because it’s money over sport.

But since it's a business, antitrust laws apply. There are suggestions that unfairly closing off market entry, Andretti may have a good case at its hand, now that his team cleared the FIA sporting rules. Previously Michael Schmidt also referred to a EU court case in that area but didn't specify which exactly he means. I found one from 2008 about some motorcycling competition in Greece but don't enough of the legalese to confidently say that this is it.

Even with smaller cars drivers haven’t seen the lines under their tire since at least the mid 90’s anyway.

F1 drivers say in interviews that especially with the 2022 regulation cars (bigger wheels, that flap on top of them) the lines are hard to see. They can actually compare to 2021 cars.

It could be that they know they will be required to anyway

The requirement will only be there for 2025. For 2026 there will be three engine suppliers with only one team, Alpine/Renault, Audi, and Honda but Honda is GM's IndyCar competitor, so that one is ruled out.

I suppose the lack of interest from Renault to renew the contract indicates they wouldn’t be required to supply Andretti.

"Renault, alias Alpine, does not want to get caught in the crossfire of a power struggle between the FIA and FOM."

They'll renew the deal once it's clear if Andretti enters or not. They want a customer. Having two fewer cars hurt their reliability.

And the deal also included the rebranding of the Renault PU as Cadillac. Andretti wanted to sell this as bringing a new constructor to the sport.

That's not true. They stated towards the press that GM will be involved in technical aspects without going into details but it's not really that hard to guess with parts those are:

GM has the facilities such as including several wind tunnels, aerodynamicists, engineers, and so on. At the very least the GM facilities will be used, potentially some personell as well.

Alfa Romeo is not involved in Sauber's technical aspects at all. GM's involvement will definitively be more than that.