The fix is divided in two parts, as a prerequisite disable SIP for now:
1. Fix the installer
A. Download pacifist
https://www.charlessoft.com/cgi-bin/pacifist_download.cgi?vers=3.6.2&type=zip install it and after mounting the matlab_R2021b_maci64.dmg go inside the icon InstallForMacOSX.app -> Show package contents -> Contents -> MacOS, open InstallForMacOSX with Pacifist;
B. Drag the InstallForMacOSX root folder to your desktop and rename it to InstallForMacOSX;
C. Overwrite the two files libtbb.dylib and libtbbmalloc.dylib inside Desktop -> InstallForMacOSX -> bin -> maci64 with my two patched revisions attached here;
D. Launch InstallForMacOSX.app inside your extracted desktop InstallForMacOSX folder and install whatever component you want.
2. Fix the actual installed app
A. Go inside your Applications folder -> MATLAB_R2021b.app -> sys -> os -> maci64 and replace the libiomp5.dylib with my patched revision attached here;
B. Again go inside the Application folder -> MATLAB_R2021b.app -> bin -> maci64 and replace libtbb.dylib, libtbbmalloc.dylib, mkl.dylib, blas.spec and lapack.spec too;
Launch MATLAB_R2021b.app and issue the command t=bench to execute a functional test and a benchmark for the most common functions.
Feel free to post your screenshots here for comparison, this is mine after the latest tweaking:
Notes:
1. The patched libs are the original libs supplied with this particular version of Matlab but patched to only redirect properly the Intel Fastmem / Fastmemcpy routines on AMD Hackintoshes and to mimic a "true" Intel CPU;
2. The new fixes make this function perfectly working, even when A is a 3x3 matrix:
[Q, T] = schur(A);