Encountered same issue here. Forturnately, the workaround works for me.
Extra info from Pluto REPL:
From worker 4: dyld: Library not loaded: @rpath/libglib-2.0.0.dylib
From worker 4: Referenced from: /Users/lyx/.julia/artifacts/d30bf8e9f9b903de5e42ffdad9e1118722c08cd8/bin/ffmpeg
From worker 4: Reason: Incompatible library version: ffmpeg requires version 6801.0.0 or later, but libglib-2.0.0.dylib provides version 0.0.0
My Julia:
Julia Version 1.6.0
Commit f9720dc2eb (2021-03-24 12:55 UTC)
Platform Info:
OS: macOS (x86_64-apple-darwin19.6.0)
CPU: Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-11.0.1 (ORCJIT, skylake)