I'm a US permanent resident who wants to travel abroad for an extended period. How can I avoid abandoning my residency?

To avoid abandoning your residency, you can apply for a re-entry permit (Form I-131) before leaving the US. This permit allows you to re-enter the US without being considered to have abandoned your residency.

You can consider applying for a Returning Resident Visa (SB-1) if you're outside the US for an extended period. However, this visa requires you to demonstrate that you had a valid reason for being outside the US and that you maintained ties to the US during your absence

Angel is correct