I upgraded to Sequoia and now my thumb drives won't mount.

How are they formatted?

If you cannot mount it, what permissions did you change?

Your info shows a Mac mini, is that correct? If a laptop, it could be the Allow accessories to connect, but that only applies to laptops.

Do you have any software installed to read NTFS drives? If so, it may be incompatible with Sequoia. They have been known to prevent mounting when they are not working correctly. They even affect drives not formatted NTFS. Check for an update.

How is the drive formatted? Macs do not support NTFS formatted drives without third-party software.

This appears to be a MacOS Sequoia issue/bug. I don't believe it is related to Sandisk thumb drives. I have a SanDisk external drive as well as an OWC Thunderbolt RAID drive and neither will mount since upgrading to Sequoia. Disk Utility can see both drives, but they will not mount.

There is another discussion thread related to this topic as well.

I really hope Apple releases a fix soon.

Same. I use a sandisk external drive as my Time Machine and sandisk thumb drives. All worked perfectly before updating to sequoia. Now none are recognized. I've written to apple support over 30 times and gotten no response. I don't understand why I need to fix this when everything worked fine before sequoia. I don't even know how to fix it since my mac won't even load the drives.

I ended up erasing my Time Machine (losing all my previous backups) and reformatting it. Well, not exactly reformatting since I formatted it the exact same way it was before. Anyway, seems to be working fine now. But I'm not impressed with Apple's response on this. Seems like Time Machine backups would be a priority.

Updated to Mac OS 15.0.1 still does not fix this issue