@hiccup, i've set mb to id3v2.3 and mb writes multiple artists tags.
@TomK7104, i can't reproduce this mb behavior, mb writes only 1st artist to display artist on my pc.
just as a workaround, you could install
this plugin. select all tracks in your library (ctrl+A), right-click on them and select "additional tagging tools> multiple search & replace". set up MSR command as in screenshot below:

, i.e. set both "from tag" and "to tag" to "display artist", tick checkbox in the "(*)" column, search for:
^(.*?);.*$
replace by:
$1
, click "preview". you can save this MSR settings as "advanced search & replace" preset, and tick this preset in ASR command for auto-applying, so you won't need to do this replacement of "display artist" manually in future (e.g. if you add new tracks to library).