Any chance that you have a Mac with an Intel CPU and installed R 4.1 for Big Sur from mac.r-project.org? That build is only for a Mac with the M1 CPU. That would explain the "arch: Unknown architecture: arm64" error message when the R session exited with code 1.
The R for macOS Developers site has this warning:
Important: The big-sur builds are compatible with the M1 arm-based Macs only. Intel Macs are supported by the high-sierra build which works on any macOS >=10.13 including Big Sur.