How to do share files on a dualboot Windows-Ubuntu in 2021?

This question reflects that it is possible to use a shared NTFS partition on a Ubuntu and Windows dualboot to keep and share your files between the two OSes. That question dates back to 2018, though, and that is a long time.

What is, to date, the best option to

• have a dualboot Windows Professional and Ubuntu
• have both OSes access and change the files
• neither OS should have files that the other OS doesn't have

Are there any innovations since 2018 that would make this easier? Exfat, for instance? What are the options to setup such dualboot (note dualboot, not Ubuntu on Windows WSL).

Are there any innovations since 2018 that would make this easier?

No. The method is a dedicated partition formatted as NTFS mounted in both systems where fastboot is disabled on the Windows side. Linux will refuse to mount dirty filesystems (fastboot=hibernation=shutting down with a filesystem in a hibernation file=dirty).

Nothing changed in regards to file sharing.

Exfat, for instance? What are the options to setup such dualboot (note dualboot, not Ubuntu on Windows WSL).

NTFS is still the de-facto filesystem supported automatically from Linux (when the system detects a windows filesystem it will add the ntfs-3g driver). exFAT requires installing an additional driver with

sudo apt-get install exfat-fuse exfat-utils

You can expect a slight drop in performance compared to NTFS.

What I do nowadays is share through an online account. Put a file on google drive and you also have an online backup at hand.