You might try booting with the EndeavourOS Live ISO, then running this and sharing the output:
lsblk -f
What we’re looking for, is the UUID for the drive you’re having issues with. It may or may not match. If it doesn’t match, that’s the culprit.
The other thing to check would be your physical connectivity, but as you say this happened after a software update, I’m less inclined to suspect that, but keep it in mind all the same.
Number 187 reports the number of reads that could not be corrected using hardware ECC. Drives with zero uncorrectable errors hardly ever fail. This is one of the SMART stats we use to determine hard drive failure; once SMART 187 goes above zero, we schedule the drive for replacement.
Based on that, I’d recommend backing up all data important to you, currently on that drive, and retiring the drive.
Edit: After performing a backup, you can perform more in-depth tests using:
smartctl -t long /dev/sda
Performing any tests before a backup could be dangerous. Until the backup is taken, all access to the drive should be avoided.
I’d recommend performing the backup from the Live ISO environment. This will reduce load on the drive, and ensure you’re in an environment that doesn’t have any potential corruption.