Quick answer — Sumire Uesaka performed 1 anime theme, including "Ponkotsu! Isekai Theater" from Isekai Quartet 2.
Sumire Uesaka performed the anime theme songs "Ponkotsu! Isekai Theater" (Isekai Quartet 2).
Sumire Uesaka's first listed anime theme is "Ponkotsu! Isekai Theater", the ending of Isekai Quartet 2.