I followed the directions for installing on GrapheneOS. I started with my iPhone and created an account with the MySudo app from the Apple App Store. I was able to make, receive phone calls as well as send SMS messages, and I had virtual card support (at least on the surface; the feature was there).
I installed MySudo on my GrapheneOS phone (Pixel 9 Pro XL) from the sandboxed Google Play store. I have sandboxed Google Play Services running. As per MySudo's instructions, I exported settings from the iOS instance to the GrapheneOS instance. Everything appeared to import and was working fine. I was able to make, receive phone calls as well as SMS messages. The one thing that was missing was virtual cards. Strange.
So, thinking maybe it was an iOS-to-GOS problem, I installed MySudo on my stock Pixel 8a with fresh-from-zero Pixel OS installation (Android 16). I exported the settings from my iOS instance to my stock Pixel OS instance. Everything appeared to import and was working fine. I was able to make, receive phone calls as well as send SMS messages. The difference here was I did have virtual card support (at least on the surface; the feature was there).
So this time, I uninstalled MySudo from my GOS device, reinstalled MySudo from the sandboxed Google Play Store, and then I imported exported the settings from the Pixel OS instance to GrapheneOS. As above, everything appeared to work fine, except virtual card options were missing as before.
I have a support ticket in with MySudo to see if there are problems supporting virtual cards still. There are no mentions of it in any of their documentation, so hopefully I can get a good answer for you here. All information (aside from this post) is over four years old.