Yep, or a different product if you want to target authors. What else do artists buy? Premade book covers that they can put their own text on? Preset text designs that they can change in Photoshop? Page designs? Chapter break designs? Can you edit, sensitivity read? Animate book covers? Make book trailers?

You could always kickstart doing like, a remake of a city map from a popular setting for an RPG.

Given your response I doubt you really have a good sense of what the contemporary virtual tabletop RPG community needs which would create a delay while you do the research, which would be playing in a game that uses figures / battlemaps and then running a game that uses figures / battlemaps and probably getting good and familiar with at least one popular ruleset. But looking at your work you have decent potential to make nice assets that could be bought by other creators of maps, maybe have a go at doing like "a compass pack" "a frame pack" "a set of mountain brushes" "a set of rooftop brushes" kind of pieces for passive income? That would be targeting 'other artists' but there's overlap with this and virtual tabletop pieces.

Your most viable virtual tabletop product would be premade city maps, I think, you do nice accessible looking illustrations. People do sometimes buy those. But you'll have to make them higher res than the book maps (20x20 - 30x30... quite a bit bigger typically) and if you get a decent number of commissions it probably won't be worth it to dabble in making an experimental city map to resell. But if you have the time that might be something to do.

Remember if authors are your primary target audience go hang out around authors. Writer Twitter and subreddits. Author forums. Nanowrimo. Beta read. Review books. Be around for them.