Do I need to file a status extension along with the change of status application to avoid becoming illegal?

It is not necessary to file a status extension along with the change of status application, as long as the request is submitted before your tourist status expires. Since July 2021, applying for a status extension is no longer mandatory for those requesting a change of status. What really matters is that the application reaches USCIS before your tourist status expires, and that the receipt (Form I-797) is issued before that date.

While the process is pending, the applicant will be in a provisional status, meaning they are not considered illegal in the country, even though their current status has not yet been changed. This means that while waiting for USCIS's decision, the person remains legally in the United States.