A possible solution to this problem would be for Steam client to examine the file rotational in /sys/block/...:

$ ls /sys/block/nvme*/queue/rotational /sys/block/sd*/queue/rotational
/sys/block/nvme0n1/queue/rotational
/sys/block/nvme1n1/queue/rotational
/sys/block/sda/queue/rotational
/sys/block/sdb/queue/rotational
/sys/block/sdc/queue/rotational
/sys/block/sdd/queue/rotational

$ cat /sys/block/nvme*/queue/rotational /sys/block/sd*/queue/rotational
0
0
1
1
0
1

Happening here too.

Examining the rotational flag isn't useful, at least on its own – I have a DVD in the drive too, and that also is being reported as an SSD. I'd probably look at the type (assume SSD if that's missing?) and whether the device is removable.

Examining the rotational flag isn't useful, at least on its own – I have a DVD in the drive too, and that also is being reported as an SSD.

Reporting DVD as non-rotational in sysfs seems like a Linux kernel bug to me - not a Steam client bug.

lsblk -d -o name,rota is opening the sysfs queue/rotational files as well, I don't know whether it can detect DVD drives.

Examining the rotational flag isn't useful, at least on its own – I have a DVD in the drive too, and that also is being reported as an SSD.

Reporting DVD as non-rotational in sysfs

I don't recall saying that that happens. I suggest re-reading.

Examining the rotational flag isn't useful, at least on its own – I have a DVD in the drive too, and that also is being reported as an SSD.

Reporting DVD as non-rotational in sysfs

I don't recall saying that that happens. I suggest re-reading.

You should have written your post in a way that is open to a smaller number of interpretations.

I'm experiencing this as well, I'm curious if this bug is uncommon or if the lack of activity is due to few people noticing it.

$ lsblk -d -o name,rota,size
NAME    ROTA   SIZE
sda        1   1.8T
sdb        1   1.8T
nvme0n1    0 931.5G

Full System info

I encountered this bug too, in today's survey. The survey says:

Storage:
    Number of SSDs: 5
    SSD sizes: 1024G,1000G,500G,120G,0B
    Number of HDDs: 0

The 0B most likely refers to my empty CD/DVD drive. Another two drives are HDDs, one of them an external USB drive, the other one an internal SATA drive. Only the remaining two actually are SSDs, both of them SATA.

Incidentally, does this misreporting happen on Windows?

For me too, both largest disks are HDD, one of them is even USB.
Storage:
Number of SSDs: 5
SSD sizes: 5000G,4000G,2000G,250G,0B
Number of HDDs: 0
Number of removable drives: 0

@dsalt
On Windows I'm getting 0 on both SSDs and HDDs, on the same computer!

Incidentally, does this misreporting happen on Windows?

Yes. My NVMe drive (the only drive in the computer) is reported by the system as "HP SSD EX950 2TB", but my hardware survey reports:

Disk serial number hash: 9bdcbd92
Number of SSDs: 0
Number of HDDs: 0
Number of removable drives: 0

The hardware properties reported by the system look pretty generic. e.g. It's class is "Disk Drives" and I see references to "GenDisk" in the driver configurations. The only place (other than the description) where I see it report anything detailed and relevant is in Hardware Ids (reminder: Windows) where it reports:

SCSI\DiskNVMe____________________________HP_SSD_EX950_2TB_SS0411B
SCSI\DiskNVMe____________________________HP_SSD_EX950_2TB
SCSI\DiskNVMe____HP_SSD_EX950_2TB411B
SCSI\DiskNVMe____HP_SSD_EX950_2TB
SCSI\DiskNVMe____
SCSI\NVMe____HP_SSD_EX950_2TB4
NVMe____HP_SSD_EX950_2TB4
GenDisk

So, it is there, but someone more knowledgeable that I will have to comment on whether or not this stuff is standardized/consistent across devices.

yyyyupp.

$ lsblk -f -o name,rota,size
NAME   ROTA   SIZE
sda       1   1.8T
├─sda1    1  1022M
├─sda2    1    31G
├─sda3    1    20G
├─sda4    1    32G
├─sda5    1   1.4T
├─sda6    1 968.5K
└─sda7    1   327G
sr0       1  1024M

reports as 2 SSDs. BIOS booting, GPT-partitioned HDD:

Computer Information:
Manufacturer: BIOSTAR Group
Model: H61MHB
Form Factor: Desktop
No Touch Input Detected
Processor Information:
CPU Vendor: GenuineIntel
CPU Brand: Intel(R) Core(TM) i5-3570K CPU @ 3.40GHz
# [...]
Total Hard Disk Space Available: 1462411 MB
Largest Free Hard Disk Block: 253938 MB
Storage:
Number of SSDs: 2
SSD sizes: 2000G,0B
Number of HDDs: 0
Number of removable drives: 0

Just "me too"ing this one... I just had a value of 9 SSDs... 2 of them are actual SSDs (the 500G ones). the 2TB one is a HDD. The zero byte ones are a USB card reader.

Ignoring the HDD issue, the zero byte one just seems obvious to me. They're clearly not valid storage devices regardless of type, and probably should be filtered out.
If it helps, here's my lsblk output...
NAME ROTA SIZE
loop0 0 4K
loop1 0 63.4M
loop2 0 63.5M
loop3 0 81.3M
loop4 0 91.7M
loop5 0 40.8M
loop6 0 40.9M
sda 1 465.8G
└─sda1 1 465.8G
sdb 1 1.8T
└─sdb1 1 1.8T
sdc 1 0B
sdd 1 0B
sde 1 0B
sdf 1 0B
sdg 1 0B
sr0 1 1024M
nvme0n1 0 465.8G
├─nvme0n1p1 0 512M
└─nvme0n1p2 0 465.3G

Same issue.

4000GB is an HDD.
62GB is actually 64GB SD card in USB adapter.

All drives should be GPT excepting the SD.

Just got the hardware survey again, It's still happening:

Storage:
Number of SSDs: 5
SSD sizes: 18T,18T,1920G,1000G,0B
Number of HDDs: 0
Number of removable drives: 0

Got the survey for the first time in a few months myself and just noticed this issue.

Both sda and sdb are Seagate BaraCuda 7200rpm HDDs

Still an issue.

Can confirm this.

Still an issue in the latest hardware survey

Still happening in the latest survey. I believe sr0 refers to my bluray player, which is what is probably showing up as the size 0 SSD.

Can confirm this is still happening, also using Arch w/ KDE, but with the non-beta current Steam client. Just got a survey, and it detected all of my drives as SSDs (should be 1 SSD 2 HDDs)