As one last attempt to break something, swap the image referenced in the aforementioned script to something else and re-run it.The bot's avatar in Discord has not changed. The new icon loads and refreshing the page confirms that it is saved. Without reloading the page after uploading the new Discord avatar, upload a new app icon via the dev apps page and click 'save changes' again.This should be functionally the same as the OP's method of changing the avatar via a command. The bot's avatar was successfully changed in the client. Paste the bot token into the script immediately before running it. Use the API to load an avatar to the bot from a terminal via a script (shown below).

In Discord, the bot's avatar hasn't changed. Upon saving and refreshing the page, the new app icon is present.

Change the app icon on the Discord dev apps page and click 'save changes' at the bottom.

No customizations were done on the generator page - the default, 'bot' scope with no permissions, was used. The bot's avatar is the default Discord avatar as expected.

Use the OAuth link generator to add the bot account to the server.

Create a bot account under the new application.

Create a blank new OAuth application from the dev apps page.

Dunno if this will be helpful or not but I've included my full repro attempt below.

A bit confused about what the issue here is, but I've messed around a bit and didn't see anything unusual.

Discord bot tupperbox