I don't know if the couple in the first photo are flat-earthers or just t-shirt models, they're not the subject of this post, only the claim on their shirts is.
You frequently see things on forums like "once you go flat, you never go back" ...
.. so even one counterexample refutes that. One often sees responses to these counterexamples (for example, in a comment to this post), that these people were never really flat Earthers, but they never post any evidence other than their having left flat Earth, see the No true Scotsman fallacy.
To save having to look for the details each time someone claims this never happens, I'm putting them here.
The first two former flat Earthers (FFEs) appeared on the SciManDan Podcast but they also show up again in the FTFE playlist at the bottom of this article.
The first is Craig Bryan Pennock, Seek Truth Speak Truth (STST)
And this is Ranty (Flerfspective, this channel isn't available now, I don't know what's going on) who describes himself as a recovering flat Earther.
Here is a video about a FFE who goes by the name "Johnny Orbital"