P.S., I would say "not recognized as being in a supported file format". Also, able to open, but not able to read... correctly. But odd that it can't deal with the file.
Run v.in.ogr input=C:\temp\proplines.dgn output=leon. Adding the --verbose switch does not add any information. g.version -rge version=7.8.4 date=2020 revision=d8fbd49af build_date=2020-10-05 ...