Linux has support for exFAT via FUSE since 2009. In 2013, Samsung Electronics published a Linux driver for exFAT under GPL. On 28 August 2019, Microsoft published the exFAT specification and released the patent to the Open Invention Network members. The Linux kernel introduced native exFAT support with the 5.4 release in November 2019.

https://en.wikipedia.org/wiki/ExFAT

ExFAT and NTFS are in the Linux kernel already. I don't think they'd need to license them at this point.

In the kernel doesn't mean you have a license to use it.

Technically yes, but companies can join the OIN for free and ship it for free.

Lots of companies are in that list (https://openinventionnetwork.com/community-alphabetical/) including Google, Sony, Amazon, and hundreds of other companies.

How does a copyright license imply a license of a third party's patent?

Open source mpeg codecs don't come with a patent license from mpeg and friends. Neither does a open source file system driver come with a patent license from microsoft and friends.

That's GPLv3, GPLv2 (which the exFAT code was licensed under) doesn't include patent rights.