Yes, although the extension is not automatic.  In HealthCare.gov states, you must apply for the extra time using an Exceptional Circumstances special enrollment period (SEP).  You can apply for this SEP by calling the federal marketplace call center at 1-800-318-2596 (not through your HealthCare.gov account.)  You will have to attest to residing in — or moving from — areas affected by a disaster event in 2021.   Affected areas are those designated by the Federal Emergency Management Agency (FEMA) as eligible to receive “individual assistance” or “public assistance.”  So far this fall in HealthCare.gov states, areas in Florida, Hawaii, Louisiana, Mississippi, Missouri, Montana, Nebraska, North Carolina, North Dakota, Oregon, Tennessee, and Utah have been designated eligible to receive FEMA individual assistance or public assistance due to wildfires, severe storms, flooding, Hurricane Ida, or Tropical Storm Fred.  This Exceptional Circumstances SEP could also apply in other areas if they are affected by a disaster before the end of Open Enrollment.

Follow this link to FEMA-designated disaster areas for more information on counties eligible to receive FEMA assistance.

State-run marketplaces also provide extra time to enroll for people affected by disasters such as hurricanes and wildfires.  Contact your state-run marketplace for more information.