What filesystem is the thumb drive using?
Disk Utility will tell you. In the example below the filesystem on the thumb drive is ExFAT.
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You may need to enable View > Show All Devices to see the drive at all.
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The Mac will read FAT, ExFAT, HFS+, and APFS perfectly well. It will not read Windows' NTFS or Linux's Ext4, BTRFS, and ZFS natively.