For BraiNSuite 21a, you need Matlab MCR for 2019b
https://www.mathworks.com/products/compiler/matlab-runtime.html
Are you installing MCR in non-standard location? If yes, please set BrainSuiteMCR environment variable to point to the path. You can do that in Linux by
export BrainSuiteMCR=/path/to/your.mcr