Replacing the Mini vMac binary with version 36.04 completely fixed the issue.

If you too have this issue and you do not want to go the compiling route, then you can simply grab the binary here and replace your /opt/retropie/emulators/minivmac/minivmac with this one : https://www.macintoshrepository.org/25178-mini-vmac-for-raspberry-pi-retropie

Because it's not an issue with Retropie, it's just that I did not initially understand how to use Retropie :P There is no technical information to fix an issue here, just me, asking a somewhat stupid-ish question that I could have solved by reading the getting started guide more carefully haha! Thank you tough for replying! Now I am becoming a master Retropie'er :P