Earlier quoted context omitted.
No, you can't be sued except by the regulator, who will only do so if you ignore them! Their role is to make you compliant, not punish you.
Where in the law does it say they only do this when ignored? Surely if this were the case, they'd put it in the law like they did punishment limits. Or are you banking on subjective enforcement?
https://gdpr-info.eu/art-12-gdpr/
"The controller shall provide information on action taken on a request under Articles 15 to 22 to the data subject without undue delay and in any event within one month of receipt of the request. That period may be extended by two further months where necessary, taking into account the complexity and number of the requests."