I use https://github.com/jackmoore/colorbox and my project includes jquery.colorbox.js (as example)
In the past I use a compiler from 2015 with

java -jar compiler.2015.jar --language_out=ECMASCRIPT6 --compilation_level SIMPLE_OPTIMIZATIONS --js jquery.colorbox.js --js_output_file output1.js

Now I updated to compiler version v20210907

java -jar closure-compiler-v20210907.jar --language_out=ECMASCRIPT_2015 --compilation_level SIMPLE --js jquery.colorbox.js --js_output_file output2.js

EDIT: With closure-compiler-v20201102.jar its working

I get no warnings or errors in console, but the demo not working with "output2" but working fine with "output1". Something the compiler is doing is optimizing incorrectly. I get the overlay and box, but no image is included.

output1

output2