Sorry for the late reply. I talked with engineering about this.
% nvfortran -c ~/tmp/len_par_tbp_02_pos.f90
NVFORTRAN-S-0155-Unimplemented feature - PDT appearing as a type spec in an expression (/home/mcolgrove/tmp/len_par_tbp_02_pos.f90: 17)
NVFORTRAN-F-0155-Type specified in CLASS IS must be an extension of type t$pt (/home/mcolgrove/tmp/len_par_tbp_02_pos.f90: 17)
NVFORTRAN/arm64 Linux Rel Dev-r251015: compilation aborted
We are unlikely to support PDTs with the select type construct, at least with the current nvfortran. We’ll be moving to a new flang based front end which will replace nvfortran. In talking with our flang team, they will likely implement it at some point but not in an early release given the complexity of implementing this support.