What can a co-founder do to have a say in the company when everything goes in favour of the main founder?

What if there is a disagreement?

Looks like there is one already.

If the situation is not acceptable to you, ask for a modification of the terms that will create a win-win situation, or leave.

Look at this answer that will provide you with additional info on partnering.

LEGAL PROTECTION. Even minority partners have rights. FOr example:

That means the main founder can withdraw all the cash without the consent of the co-founder.

The word for that is theft. A foutner in some countries may find himself thrown out of the company at book value (and prosecuted by law). Criminal charges.

Why? Because even if the co founder only owns 1% of the shares, he has a right to 1% of the assets. Stealing them and running is illegal.

So, there is quite a lot of legal protection. You dont enter partnerships in a vacuum.

I'm sorry to say this but, from your post, i would say you are not a co-founder nor treated as one. If the founder can do everything without your OK then leave, you are doing nothing there, sooner or later he will takeover. Unless you can balance the partnership, as you describe it, it's pure non-sense.

Who has control of the bank account is not particularly relevant. Even a sole founder with full access to the company bank account doesn't have the right to take the money and cash it for himself.

Why? Remember that the company is a separate (moral) person. He'd be stealing from that person. Yes, it's weird because he is the company's only founder, but it still must be treated as a separate person.

What really matters is who controls the company itself. That usually depends on your corporate structure, who has how many shares, whether this is some kind of board of directors and so on.