preview_OptiFine_1.21_HD_U_J1_pre6

 - restored vanilla check for invalid resource pack paths
 - fixed CEM parameter frame_time to follow tick rate
 - fixed cape button in skin customization
 - fixed CEM for block entities
 - fixed Quick Info to show frame time
 - updated CEM animations to use global update per model
 - added CEM parameter "frame_counter" and function "ifb"
 - Fixed CIT enchatments
 - fixed CIT models
 - fixed CEM models
 - fixed shaders attributes
 - fixed Anisotropic Filtering and Antialiasing
 - fixed GUI text color
 - updated to 1.21
 - not compatible with Forge