Most of the listed devices are 5 or 6 years old.
I'm curious about the reason for that particular set of phones: T-Mobile says this isn't specifically lack of VoLTE, and the list is far too small for it to be that.
When Sprint issued a list of phones that would no longer function (the obsolete OMA list), it was apparently because of a change in the route they were using for over-the-air provisioning, and the obsolete phones not being able to access the new route. But T-Mobile doesn't do provisioning that way, although it might still be tied to updating a profile or something similar.
Below is an updated article, that also isn't clear, seems to say all non-VoLTE supported phones, including the particular set listed above, will no longer work on T-Mobile network after Jan 29, 2021. Free replacement phones for current customers with non-VoLTE supported phones.