Problem running post-install step. Installation may not complete correctly

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1

I get 75% through installing ArduinoCreateAgent and this pops up:

Problem running post-install step. Installation may not complete correctly
Error running C:\Program Files/certmgr.exe -add "C:\Program Files/cacert.cer" -s -r currentUser root: child killed: unknown signal

2

Going to point you here first as there is some quite vital information missing.

Without the Certificate you will be unable to run CREATE properly.
But with the extra info it should be easy enough to guide you a little better.