The Multimine 1.16.5 jar on curseforge was compiled with java 11 making it incompatible with java 8 which is still commonly used for Minecraft versions up to and including 1.16.5.
latest.log showcasing crash
it should be recompiled with java 8 for better compatibility, as jars compiled with java 8 can be run on java 11 but not the other way around

d8e2eb1
should fix it