One common theme is self - discovery. Many fanfics focus on Cheryl finding out more about herself, her strengths, and her weaknesses. For example, in 'Cheryl's Inner Journey', she embarks on a trip to understand her own emotions better. Another theme is family drama. Given Cheryl's complex family situation in the original series, fanfics like 'Cheryl and the Blossom Family Secrets' explore this aspect further. Love and relationships are also common, as seen in 'Cheryl's Romantic Escapades' where she experiences different types of love.
In Cheryl Blossom OC fanfiction, a frequently seen theme is the power dynamics. Cheryl comes from a wealthy and influential family in Riverdale, and when an OC enters her world, it creates an interesting shift in the power balance. Sometimes the OC is from a different social class, and how they navigate this difference with Cheryl is a big part of the story. Another common theme is family. The OC might have a different family situation compared to Cheryl, and how their families interact or how the OC affects Cheryl's relationship with her own family can be a central part of the fic. There's also the theme of mystery. Some fics make the OC have a mysterious past or purpose in Riverdale, and Cheryl gets drawn into solving that mystery.
One great 'Cheryl Blossom and Toni Topaz fanfic' is 'Cheryl's Redemption'. It shows Cheryl evolving and her relationship with Toni strengthening in a really heartwarming way. The story beautifully captures their individual personalities and how they complement each other.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including Riverdale where Cheryl Blossom is from. Just search for 'Cheryl Blossom' in the search bar.