The comments of AerionFr and mr.buffed seem to imply that portfolio runs only with the Java default set to version 11, but that's not the case:
$ archlinux-java status
Available Java environments:
java-11-openjdk
java-15-openjdk (default)
Portfolio runs just fine with Java 15 as RTE. I have still no idea what is wrong in your case.
Pinned Comments
Cobra commented on 2023-08-19 13:34 (UTC)
Thanks to Bevan, we now have a simple and elegant (compared to my attempt) workaround that lets the PKGBUILD download and use the most recent version of maven (currently 3.9.4). Should not need any intervention from you. :)