Keylogger on old iPad ?

Hi, thanks in advance for your help. I got an email saying that a key logger was put on my device. It's a super old iPad, model MD334LLA/A, last available update for the model was 9.3.5

The email was sent from my own email account, which I should have deleted a long time ago, but didn't. The security on it was nil (four digits) so it's obviously vulnerable too.

I never use the old iPad except for a an old recipe app, so there can't be much key logging data to have taken.

The question that is killing me is if the keylogger software can see across devices. I want to know if password updates are safe to do on my newer, up to date iPads or iMac.

Thanks very much for your replies.