#2xz-3z+8x-12y# cannot be factored by grouping.
#(2xz-3z)+(8x-12y)#
#=z(2x-3)+4(2x-3y)# The expressions in parentheses are not the same, so we cannot factor any further.
If we had started with: #2xz-3color(red)(y)z+8x-12y# , the we would get:
#color(white)"sssssssssssssssssssss"# #(2xz-3yz)+(8x-12y)#
#color(white)"ssssssssssssssssss"# #= z(2x-3y)+4(2x-3y)#
#color(white)"ssssssssssssssssss"# #= (z+4)(2x-3y)#