>>In the screen with the transfer speed, maximum speed reached is abysmal - but could be the result of only copying / writing smallish data or checking too soon after install. Check again after 1/3/6/12/24 H of normal work (unless you opt for saving data first, which I cnsider more important) and if it stays that low, create your own test. Transfer speed usually rises with file size - you c/should create a tiny bench for yourself by creating a known directory offline with perhaps 10 GB size of files [10 KB, 100 KB, 1 MB, 10 MB, 100 MB, 333 MB, 1 GB ] and measure speed / time taken to copy.
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>Yes, it was low. After a few minutes, during all that time, today shows a more respectable value. I have attached an image.
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>>If anything in Als list offers an option to log disc and CPU temperature for later analysis, go for it. If sensor data for other I/O areas is available, add.

Maximum transfer rate for consumer SATA SSDs should be around 400 - 500 MB/sec. Your image shows 43 MB/sec.

It may be that there is so little disk activity you're not seeing the full performance of the drive. You could try running one of the disk benchmarks like Crystal, or you could do a backup (e.g. image backup) to external media.