Hello @Courtney Regan !
I understand you need to block IPv6 for specific browsers and not on OS level
one suggestion is to use the Windows Advanced Firewall Rules
here is my example :
Create a new Outbound rule , Custom Rule , Select the exe file of the Browser and if you want the source or destination endpoints !
that simple!
Let me know if you need more details!
I hope this helps!
Kindly mark the answer as Accepted and Upvote in case it helped!
Regards