encryptpad is a custom build using AUR build script → AUR (en) - encryptpad
botan2 is not yet in stable → Packages
So you have to wait until next stable snap - or switch to testing branch - you decide.
EDIT:
Package build as expected on unstable branch.
$ pamac build encryptpad
[...]
==> Creating package "encryptpad"...
-> Generating .PKGINFO file...
-> Generating .BUILDINFO file...
-> Generating .MTREE file...
-> Compressing package...
==> Leaving fakeroot environment.
==> Finished making: encryptpad 0.5.0.2-11 (søn 21 maj 2023 14:53:15 CEST)
==> Cleaning up...