The Swedish Migration Agency, which is the responsible agency for these questions, informs as follows:

Individuals who can prove that they are not able to leave Sweden due to for example cancelled flights can, upon submitting an application, be granted a visa extension provided the total length of stay in the Schengen region will not exceed 90 days.

If the stay in Schengen will exceed 90 days, an application for a visitor’s permit must be submitted.

An application to extend a stay in Sweden is to be submitted before the expiry of the current allowed stay.

See the link below for further information.

https://www.migrationsverket.se/English/Private-individuals/Visiting-Sweden/Extend-a-visit.html

Best Regards