Hmm, I can not replicate your issue. I wonder if this is because the latest SSE code uses new features of the compiler. What happens if you delete line 18 of nifti.pas:
  {$DEFINE SSE}
and recompile. This will provide full functionality, but will not use the faster rescaling. 

Please confirm that your computer works fine with the compiled version here (v1.2.20201102):
  https://github.com/rordenlab/MRIcroGL12/releases
If so, you may need to simply wait for the next stable Lazarus/FPC upgrade, or move your development to trunk. Working with Gareth Moreton, the latest code leverages advances CPU features and also compiles on the upcoming Apple ARM-based Macs. These cutting edge features may make it hard to compile with the current versions of the compiler and IDE. However, they do provide a profound benefit for the users, with many of these functions becoming memory rather than CPU bound.