I did not encounter any problems with the instructions but whenever I reach the solver stage the program just continues to lag heavily.
Whenever I move the courser to select anything after the first solve was completed it just lags.
It is also true for MATLAB window. But any other software running works properly, even if lagging MATLAB is still opened.
I have re-installed Matlab and re-installed the FEATool but to no avail. Any ideas are welcome!
Thank you for reporting the issue. Could you confirm that you mean lag as in the GUI interface lags (when pushing buttons etc)? Unfortunately this is hard to debug without having direct access to your specific system.
As for UI responsiveness I often recommend installing and using Matlab R2011b which generally is significantly more responsive with later versions, see (you have multiple Matlab versions installed at the same time):
If you have the Windows Subsystem for Linux (WSL) you can also try running in that (both Matlab and FEATool can be installed and run graphically in WSL if you also install an X11 display server such as VcXsrv).
Just to update, this issue was likely due to updated Matlab interfaces for Mex libraries causing incompatibilities on certain cases with external linear solvers such as Mumps. For Matlab 2020 and later the linear solver will now default to the built-in ones (Umfpack/Suitesparse) with the new build, available from the GitHub repository (v1.13.1 Build 21.02.048):