Drobo not detecting a drive and shows as red

drobo wasn’t mounting properly it was showing up as a drive but not in drobo dashboard or the drobo icon when loading, so I rebooted everything and then finally got a notice that I needed to updated the firmware on my Drobo gen 3 and all drives where green and working then later in the day one of the drives is now red and in drobo dashboard it says there is no drive there and that it is critical I place a drive there. I am afraid to remove the drive do not want to lose my data! What do I need to do? How could my drive which is the newer ones have failed just like that? Is that what it means, that the drive has failed?

One light red beside a particular drive generally means that drive has failed & needs replacing yes.
How it could have failed, could be literally any of the many causes for drives failing, it does happen with any age drives, even with brand new ones.

The safest thing to do is what dashboard is telling you to, replace the drive it says has failed, just swap it for a new one, but make sure the new one doesn’t use SMR as it’s recording technology. You don’t even need to shut down, just swap them & wait a little while for the unit to notice, the lights will probably all start flashing while it rebuilds at that point, depending that stage could last a long time.

Apart from having to mess around to make it show up (not all that uncommon) everything since it did is pretty much normal ways for a working Drobo to behave, including what it does if a drive fails (depending how the drive failed).

It’s far more likely that it’s a drive failed than anything else, that is what it’s telling you, exactly as it’s supposed to. It’s possible to be a different cause, but you’d still need to replace that drive to find out.