Hi, thanks for reaching out. It looks like you created a model using the form recognizer v3.0 API. With v3.0, you can create a model with just a name, it doesn't require GUID like in v2.0. Even when you list the models using v3.0 Api, GUID will not be available. Basically this is a scenario where power automate wants GUID because it has not been updated to use v3.0 API of form recognizer.
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if the reply is helpful. Thanks.--