I’ve got it working now – thanks so much!
I changed only the first link to HTTPS in the Discourse code block. Since this site is transitioning from HTTP to HTTPS, all previously created topics had a discourseEmbedUrl of http:// sitename.tld/node/blablabla. Changing that to https made the topics appear to be recreated. So I ended up changing only the discourseUrl to HTTPS, and leaving the discourseEmbedUrl in HTTP to preserve previous topics.
Thank you again! I hope this is helpful for anyone facing a similar transition 