New social media platforms come and go - and change in popularity - all the time. The best way to find out about new platforms is often on existing platforms. For instance, an artist may tweet about content they have just added to a new platform.
Equally, people you already follow are often the best source of leads to new people to follow. A blogger of interest to you will probably link to other relevant blogs.
Alternatives to X (Twitter) are discussed in this article from November 2022.
The Instagram Guide for Galleries is produced by Artsy and is free to download.
Mastodon is discussed in this article, which lists many resources for making the most of this platform.
Pinterest is a huge website, mainly for sharing images found online. Pinterest is best-known for consumer products, but is so big that the amount of art-related content is still very large.
Different platforms are popular in different countries. For instance, Weibo, often described as the Chinese-language X (Twitter), is important in China.