Okay, that was spot on guidance @alejandror.
I made the change per the load balancing instructions on the link you shared and it worked.
Specifically, in case someone else needs these steps in the future:
sudo nano /opt/bitnami/apps/wordpress/conf/httpd-prefix.conf
Then adding this line at the top of the httpd-prefix.conf file:
SetEnvIf x-forwarded-proto https HTTPS=on
Then restart Apache server:
sudo /opt/bitnami/ctlscript.sh restart apache
Tested it with Network console open and it looks good! (no more HTTP mixed content errors).
To make sure it wasn't this setting doing anything, I also turned off "Opportunistic Encryption" on Cloudflare.