Wow...looks like I don't do much disk I/O compared to most people here. I'm on a 2017 iMac that I use for both personal stuff and work. It seems like most people here can do in a few months what it took me 5 years to do.

  Critical Warning:                   0x00
  Temperature:                        39 Celsius
  Available Spare:                    100%
  Available Spare Threshold:          10%
  Percentage Used:                    2%
  Data Units Read:                    163,453,178 [83.6 TB]
  Data Units Written:                 96,776,875 [49.5 TB]
  Host Read Commands:                 4,760,816,278
  Host Write Commands:                3,237,489,546
  Controller Busy Time:               7,045
  Power Cycles:                       16,947
  Power On Hours:                     2,307
  Unsafe Shutdowns:                   109
  Media and Data Integrity Errors:    0
  Error Information Log Entries:      0

I've got 64 GB of RAM so don't have much swap usage which probably helps.

I see everyone posting data for M1 Macs has an "Available Spare Threshold" of 99% whereas I've got 10%. What's the story there?

My understanding is that you want "Available Spare" to be as high as possible, and "Available Spare Threshold" is how low "Available Spare" can go before it is considering to be a failure, so the lower "Available Spare Threshold" the better.