In the early days of Stardew Valley modding (circa 2016), a mod was released that allowed players to date and marry Jas.
Most players seeking "Jas mods" aren't looking for romance but rather to improve her role in the game’s family dynamics: stardew valley jas marriage mod
If you want to enhance your interactions with Jas without violating community guidelines or platform rules, consider these legitimate alternatives: In the early days of Stardew Valley modding