I reinstalled R and all packages from scratch, but I still had the error. I can reproduce it in your cloud tutorial so I don't think it's my setup https://rstudio.cloud/project/3946303:

install.packages("targets") # to get the latest release
library(targets)
tar_make()
tar_load_everything()

Error:
! branches not in metadata: branches out of range

Stepping through the code it does seem that tar_load_raw is being passed names from meta that aren't targets. The "branches not in metadata: branches out of range" error is the same one I get if I try e.g. tar_load(get_data).