A resource pack made for 1.19 does not function properly in 1.19.3. Many broken or missing textures.
Comments 3
The resource pack format has changed and thus resource packs need to be updated for 1.19.3. Your resource pack should either show up as incompatible ingame, or it has not been updated correctly by its author.
Intended, read the changelogs: textures need to be added to the atlas via the atlas json files, if not in the block or item folder. This was a change made to vastly increase resource loading performance.