When calling arMyStr2Sym the function call fails. The problem seems to be on line 17
if(str2double(matver.Version) >= 9.4)
It branches into the else caluse and causes further problems with symbolic conversions for Matlab version 2021a as matver.Version value is '9.10' and str2double(matver.Version) equals 9.1, which of course is smaller than 9.4.
Possible solution is using verLessThan function (for example "if(~verLessThan('matlab', '9.4'))" ) or something similar.
verLessThan is added in R2007a so there should be sufficient backwards compatibility.