Not undertale related, but apparently Toby Fox was the composer for the new Pokémon game : r/Undertale

Undertale's Toby Fox Composed Some Of Pokemon Scarlet and Violet

Undertale Creator Toby Fox Is Composing Music for Pokemon Scarlet

Exl Informer Game by Exlreview - Issuu

This is why I love Toby. : r/Undertale

Undertale's Toby Fox has songs in Pokémon Scarlet and Violet - Polygon

Nintendo Direct, September 4, 2019: Information and Reactions

Toby Fox in Pokemon Scarlet/Violet (Via Undertale newsletter) : r

Pokemon Scarlet & Violet To Include Music By Undertale Creator

10000 best New Pokemon images on Pholder

Pokémon Scarlet and Violet Review - IGN

Pokemon Scarlet & Violet Will Feature Ed Sheeran's New Song

Undertale's Toby Fox Composed Music For Pokemon Scarlet And Violet