The dock itself accepts only bare 2.5" drives (I've only tested it with SSDs since I haven't used HDDs in years) so I can't connect an SSD in an enclosure to it (nor would I want to; besides, even if it wasn't physically impossible with my dock, it would be silly to connect an enclosure to it). Also, keep in mind this dock has two parts--the stack (or sandwich) of truncated enclosures and the Thunderbolt hub--that are kept connected together at all times on top of my desk (disconnecting and reconnecting the two parts is too much of a hassle so I consider them to be permanently connected).
The Thunderbolt hub part of the dock is another story. With the dock attached to the hub, the only ports still available are three additional Thunderbolt ports on the back of the hub. I don't know if they can be used as USB 3.1 Gen 2 ports or not. Even if they could be, I wouldn't be able to get at them without a lot of hassle and tying up far too much space on the top of my desk and the whole point of the dock I built is to be as hassle free as possible and take up as little space as possible.
Then there is the matter of bandwidth. While the thunderbolt hub is rated for Thunderbolt 4 (and is backwards compatible with Thunderbolt 3), I'm feeding it from a Thunderbolt 3 port on my laptop. That limits me to only up to 20gbps of bandwidth. With four SSDs plugged into the dock, I could be consuming 5Gbps bandwidth per SSD which would max out the available bandwidth. Adding anything more would probably slow everything down.
Now, if I took leave of my senses and connected an SSD in a non-TRIM compatible enclosure directly to the Thunderbolt hub and ran the TRIM command, I would either get an error message or it just wouldn't show up as being TRIMmed (it's been long enough since I tried running TRIM on an SSD in a non-TRIM compatible enclosure, I just don't remember which; of course, with my ADHD, that could have been yesterday ). I only have TRIM compatible enclosures.