It looks like Brave on iOS does not support authentication through client SSL certificates like it does in the desktop app.
This is supported in Safari on iOS through configuration profiles: I can install a .p12 client certificate on my phone, and this will automatically be used on websites that have SSL client verification enabled.
It seems like you’ve identified that Brave on iOS currently lacks support for client SSL certificates, unlike its desktop counterpart. While Safari on iOS does support client SSL certificates through configuration profiles, the same functionality is not exposed to other apps, including Brave.
For a more detailed and accurate solution, you may want to discuss this with the Brave community or development team. They might provide insights on any ongoing developments, workarounds, or plans to support client SSL certificates in future iOS app updates. Your findings and input could be valuable for others facing similar challenges.