But I thought my external HDD was ok. Also, when I buy a new laptop, should I buy one with a SSD NVMe?
You could also wait until it dies. But with 10 years age, this won't be long, as there are limits on how long hardware, especially with moving parts, can operate. I'm fairly certain that each and every halfway-decent laptop you buy today has at least one M.2 NVMe drive. Only the real cheap bargain stuff might still have SATA drives.
So, it looks HDD Sentinel only makes a projection like you said, since it states my external HDD will last more than 1000 days.
With perfect readings, it cannot predict anything. It tries to guess the fate of the drive from fails already present.