I've also had them running at 50 degrees for some time, but you should bear in mind that this may have a negative effect on the lifespan. Alternatively, you could just leave the HDD housing open?

I agree with the answers of the other users.

The hard discs do a "thermal recalibration" which means that the surface is recalibrated so that the track is hit.
The higher temperature causes the tracks on the platters (discs in the hard drive) to be shifted, and the hard drive always recalibrates when the temperature changes. This means a short time-out when accessing the disc, normally this is done in standby, but can also occur when it is accessed. This is problematic if the disks are running in a network via a raid controller, the raid controller thinks that the disk is no longer working properly and degrades the raid status.

The disc is reported as defective and later the disc is fully functional but the raid stack is no longer redundant.
The server manufacturers have customised firmware on their hard disks to tell the raid controller that this is being done.

There used to be discs (especially from Micropolis) that were sold as AV discs for Adio/Video Recordig. These discs had a reduced calibration in the firmware to prevent frame drops or record drops.

It is therefore better not to operate the discs outside the manufacturer's specifications, or only to a limited extent, in order to avoid damage or data loss.

No, I wouldn't do this with any hard drive in the long term. The resulting temperature must be dissipated. For a short time, yes, but not in continuous use.

I would like to say yes, but I simply don't know. I have it in a normal PC case and I don't need it for other purposes (yet).
If you use the disc in an external housing, there shouldn't really be a problem. So I would try that.
Of course, protect the housing from sunlight and don't store it on a radiator. This disc is also sold in external drive housings. It is also designed for 24/7 operation. So it should be able to withstand a little bit.
It should be clear that too high a temperature is not conducive to a long service life.

4 disks in enclosure currently running at 38C. Not sure what is the temp ceiling, but never had an issue, even approaching 50C

root@local[~]# ls -1 /dev/sd? | xargs -n1 smartctl -A | grep Celsius
194 Temperature_Celsius 0x0022 100 100 000 Old_age Always - 38 (Min/Max 21/46)
194 Temperature_Celsius 0x0022 100 100 000 Old_age Always - 38 (Min/Max 22/48)
194 Temperature_Celsius 0x0022 100 100 000 Old_age Always - 37 (Min/Max 21/47)
194 Temperature_Celsius 0x0022 100 100 000 Old_age Always - 37 (Min/Max 22/47)