One (910-006630) it's the EER (Europe East) version, the other (910-006631) the EWR (Europe West) version as mentioned by another community answer. There's no technical difference, the price difference is due to the price from each supplier.

This is the same mouse, only our suppliers are different, hence the price difference.🫡

Yes, that is correct, the side buttons cannot be removed, as is possible with the G Pro.

Most likely just the packaging. One (910-006630) it's the EER (Europe East) version, the other (910-006631) the EWR (Europe West) version.