I have used
:visited in CSS for links for a long time and understand their value. However I have not thought of using it for buttons. My "CTA buttons" are usually soft CTAs that direct to valuable information. They are on cards near the second half of the page to engage the user one last time before they leave.
This is not used often for primary CTAs but helps people still looking for health information before committing to coming in for a visit.
The big question is have you ever used
:visited on buttons?
I have not seen much research around its usage since the CTA tends to be a step you don't want them to return from but have them continue. These CTAs are there to maintain engagement and encouraging them to learn more by going to another and another until they have all the knowledge they need. Maybe these are not truly CTAs, so don't get caught up in that, but ultimately have you seen buttons with
:visited styling and has the helped or hurt?