Nesting issues

Thank you for your explanation, but not everything is clear to me.
For the following questions I refer to your formula in cell C4.

 1: '=if(d4="",0,if(d4="hol",0,if(d4="mu",0,if(d4="max",0,if(d4="off list",0,if(d4="rdo",8,
 2: if(d4="10list",                                                        (averageifs($b4:$p4,$b$3:$p$3,"ot w",$b$2:$p$2,"12",$b4:$p4,">2.00")-$b4),
 3: if(or(d4={"ref","otdt"},and($b$2:$p$2,"12",$b$3:$p$3,"ot w",">2.00")), (averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">2.00")-$b4),
 4: if(or(d4={"ref","otdt"},and($b$2:$p$2,"10",$b$3:$p$3,"ot w",">2.00")), (averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">2.00")-$b4),
 5: if(or(d4={"ref","otdt"},and($b$2:$p$2,"12",$b$3:$p$3,"ot w","<=2.00")),(averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">0.17",$b$3:$p$3,"ot w",$b4:$p4,"<=2.00")-$b4),
 6: if(or(d4={"ref","otdt"},and($b$2:$p$2,"10",$b$3:$p$3,"ot w","<=2.00")),(averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">0.17",$b$3:$p$3,"ot w",$b4:$p4,"<=2.00")-$b4),
 7: if(or(d4={"lv","sc"},   and($b$2:$p$2,"12",$b$3:$p$3,"ot w",">2.00")),  averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">2.00"),
 8: if(or(d4={"lv","sc"},   and($b$2:$p$2,"10",$b$3:$p$3,"ot w",">2.00")),  averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">2.00"),
 9: if(or(d4={"lv","sc"},   and($b$2:$p$2,"12",$b$3:$p$3,"ot w","<=2.00")), averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">0.17",$b4:$p4,"<2.01"),
10: if(or(d4={"lv","sc"},   and($b$2:$p$2,"10",$b$3:$p$3,"ot w","<=2.00")), averageifs($b4:$p4,$b$3:$p$3,"ot w",$b4:$p4,">0.17",$b4:$p4,"<2.01"),0)))))))))))))))

Looking at your formula it seems that if the code is not 10LIST you don't want to distinguish between the 10's and 12's.
After all, the averages in lines 3 and 4 are the same.
This also applies to the averages in lines 5 and 6, the averages in lines 7 and 8 and the averages in lines 9 and 10.
Is that right?

I don't understand when exactly which average should be calculated.
Your condition states something like >2.00 and <= 2.00, but it is unclear to me what should be >2.00 or less than 2.00. [In case of the formula in C4].
Even if the reference is to multiple numbers, what should happen when part of those numbers is greater than 2 and another part is less than 2?
After all, only 1 average can be calculated by the formula.

In addition, the conditions you mean must be written down in a completely different way.
The condition in line 3 always returns TRUE (to my surprise, because I expected an error).