Welcome to the community @violetcroc11!
There is qubes-issue #6792 fixed on Aug 1st, which solves heads #789. This means you will have to use RC2 to install R4.1.
However, if you do a fresh install of R4.1 it will use cryptsetup2 which is not supported by the coreboot version that is build into your heads version. So you will need to wait until pull request #1015 was merged into heads. Then build it and flash it on your NitroPad. See also this thread with the answer from Thierry Laurion containing the above information.
It is my understanding that the only way (that doesn’t involve building and flashing a custom heads version) to install R4.1 on your NitroPad right now is to do an in-place upgrade from R4.0.