If you use uBlock (or something like it), you can make a custom filter to block moderators when they’re not acting as mods.
Change out THEIR_USERNAME with their name, and keep everything else intact.
To block their posts (not new topics, but comments in existing ones):
! Block SDMB posts by their user ID. Excludes mod notices.
boards.straightdope.com##div.topic-post:not(.moderator):has(a.trigger-user-card[data-user-card="THEIR_USERNAME"])
An optional second rule can also block quotes of their posts in subsequent comments, but I don’t recommend this. It makes other posters’ replies confusing, because you have no idea what they’re replying to anymore.
! Also block quotes of those posts in subsequent comments.
boards.straightdope.com##aside.quote[data-username="THEIR_USERNAME"] > blockquote > *
This does NOT block any posts flagged as an official moderator note.
And you can use this last optional rule to block ALL topics (new threads) started by them. But this is also not recommended, since this will accidentally hide their moderator announcement topics too… I don’t think Discourse differentiates mod vs non threads at the topic level, only the post level.
! DANGEROUS: Also block ALL topics started by this user, regardless of mod status.
boards.straightdope.com##tr.topic-list-item:has(td.posters>a:first-child[data-user-card="THEIR_USERNAME"])