An expired green card does not mean you lose your permanent resident status. You are still a lawful permanent resident, but you need to renew the card as proof of status.

You should file Form I-90 to renew your green card as soon as possible. Once you file, you’ll receive a receipt notice that can be used together with your expired card for work and travel purposes.

Many people panic about this, but it’s very common. The bigger issue is delaying too long, especially if you plan to travel or apply for citizenship later.