Filesystem advice requested

So, I'm resetting a machine for a friend. Currently on Win10, has 500G SSD and a 1TB spinny installed. He's looking to move to Linux ("something KDE") but wants to keep Win10 in the wings just in case. He also has half a metric shit-ton of assorted music, video, whatever files that he'd like full access to.

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My plan is to split the HDD, clone his Win10 to one partition, install whatever distro he decides on on the SSD and use the rest of the HDD as a common data store. So that's the situation.

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Seeking opinions on the best format for that data partition, as I have not kept up on filesystem shortcomings. Last I heard NTFS isn't thrilled with Linux, Windows isn't thrilled with Ext4, exFAT has never been a favorite of mine, and FAT32 may be too limiting for him. Is this still accurate?

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Your thoughts, please and thank you.