zinc pallete/texture from Create: World of Color
deepslate, tuff, calcite smooth basalt from Programmer Art Continuation Project.
grooved ice textures based off the first known textures of glass, recreated by Capopanzo on the mc wiki
some textures based off of ones from the "Reminiscence" modpack's custom resource pack
sculk jaw based off/edits of recreations of textures seen in mc live 2020 - recreations made by Maksom4ik, and Deshman-gpuser on the mc wiki
caverns & chasm's Mime & Peeper textures based off the Skeleton and 'Observer' mob textures from the Cypress build of Alpha 1.0.16.05, a presumably completed ARG about a forgotten, obscure branch of alpha builds. The mime is aditionally using textures from the Bogged skeleton's textures in Programmer Art Continuation Project.

Unrelated, but you would not believe how hard it was to get the texture for Education Edition's Glowsticks & Balloons.