Not trying to flog a dead horse, but you can put a share button on your articles on Substack to encourage your readers to share them with their friends.

Also, you can tag your newsletter with up to three topics so that when readers come to the site and search by topic, your newsletter comes up.

You can also import your archives from Medium.

A lot of the "big" writers from Medium are migrating to Substack. They are usually early adopters.

I hope that you don't mind me nagging you. I just think that it is a great platform for you. And most importantly, you can write what you want and Substack doesn't care.