Dear @Not-The-Foggiest,
we have been able to work around this issue as outlined at Some icons are not translated properly · Issue #17 · Daemonite/discourse-material-theme · GitHub the other day by adding this snippet at the appropriate place, effectively disabling the “alt-” variants of the icons to get them visible again:
// Fix MBT#17: Translate "-alt" icons to non-"-alt" ones to
// counter disappearing "edit"- and "delete"-post icons.
// https://github.com/Daemonite/discourse-material-theme/issues/17#issuecomment-479716834
classNames = classNames.replace('-alt', '');
It’s really just a quick workaround but might well help you along.
With kind regards,
Andreas.