You can travel with the expired green card with I-797 according to CBP.
Expired Conditional Resident: Two-year validity
• A Conditional Resident with an expired Permanent Resident Card(PRC with a two-year expiration date) may be boarded if also in possession of a Notice of Action (I-797).
• The Notice of Action extends the validity of the card for a specified length of time, generally 18 months.
• Do not board the traveler if they are not in possession of Form I-797.