The overwhelming majority of SSD units are 2.5" . As long as it is 9.5mm or less in height, it will fit fine. Hybrid drives (large spinning drive with a smaller SSD acting as a cache) are 3.5" most of the time, could this be where the confusion has arisen? I've got an SSD drive working fine here, however I'm not sure about TRIM command support, so I'd be careful using an SSD drive with Android for a few years, THEN making it a boot drive/critical data storage area elsewhere.
The S905 (used in the T8-S Plus) is one of the chips listed at
http://kodi.wiki/view/Android_hardware as being H265 capable, whereas the line above that has a note of 8-bit only for the older chips.
I'm sorry that I don't have a concrete answer for you right now, but if there is an objective test that can be run to test 8 vs 10-bit please do let me know, I'd be happy to run it for you on a T8-S Plus.
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I say objective as I'd not want to rely on my eyes alone to give you an answer.