FediTips , (edited ) 
If you want your post to be as widely visible as possible, you might want to use groups as well as hashtags:
➡️ https://fedi.tips/how-to-use-groups-on-the-fediverse/
Even if you have no followers, posts sent to groups will be visible to everyone following the group and also everyone on their servers.
Posts that just use hashtags will only be seen on servers that have "noticed" your account:
➡️ https://fedi.tips/which-posts-and-accounts-can-i-see-from-my-server/
In a nutshell: groups distribute posts actively, hashtags distribute posts passively. Using both is best.