The install as of very recently no longer offers Plasma under Graphical. Looking at tty3, the reason appears to be that it is looking for task-plasma5-minimal and not finding it. This is a network install, with Custom Desktop selected and all of the Workstation - Server - Graphical options selected. Probably something was never updated for Plasma6.
Thank you for the report. Your diagnosis looks good.
Summary: Install no longer offers Plasma => Install no longer offers Plasma; now 6, looks for 5Assignee: bugsquad => mageiatools