Bug error: 'str' object has no attribute '_key'

It's been a few days since I've been having problems with ML-Agents, at first I thought it was a problem with versions, projects and etc, so I tried to solve everything, but it always resulted in the same error.

when using "mlagents-learn" command to start testing, cmd always returns the same thing:


unlike other (several) tutorials on the internet that always return the message "press play to start...", this one returns that, I've looked for an answer on the internet and even found the same question on the "Code grepper" site, but no answer.

I've already tested this on unity versions of 2021, 2020, I'm using pythom 3.7 as recommended, I have a GPU (AMD radeon 6450), windows 8.1.

I went to investigate further and found this pythom code


however I don't have the slightest knowledge in pythom and i really need to use ML-agents as soon as possible, If anyone knows how to solve this problem, please help me.
(this is my first thread)