As a final note of mess, they will not be able to rotate keys/passwords in the short term (eg. the day next my quit). Some passwords have never been changed since the accounts were created, even after other employees left.

That's wrong, it doesn't make sense, and you have to pretend that they change this policy. It may seem a rude request, but the consequences if someone does damages with those credentials and accuse you may be much worse than the risk to burn bridges with the company.

I would write an email to the boss like:

Dear boss, this mail is to remember that I still have access to the following accounts: <list of accounts and credentials (or attach a file)>. Since I will leave in , I kindly ask you to take actions during this timespan to change the credentials and assign them to other people. Best regards

The last day (or a few days before), I would send another mail clearly stating that if the credentials will not be changed, I will take legal actions to protect myself.

As a final note of mess, they will not be able to rotate keys/passwords in the short term (eg. the day next my quit). Some passwords have never been changed since the accounts were created, even after other employees left.

That's wrong, it doesn't make sense, and you have to urge them to change this policy. It may seem a rude request, but the consequences if someone does damages with those credentials and accuse you may be much worse than the risk to burn bridges with the company.

I would write an email to the boss like:

Dear boss, this mail is to remember that I still have access to the following accounts: <list of accounts and credentials (or attach a file)>. Since I will leave in , I kindly ask you to take actions during this timespan to change the credentials and assign them to other people. Best regards

The last day (or a few days before), I would send another mail clearly stating that if the credentials will not be changed, I will take legal actions to protect myself.

Also, BCC both mails to your lawyer.