Hi @OlafBond
I set up a flow, you can refer to below screenshots.
Assume the file is pdf or docx and the size exceeds 50kb, the attachment will be saved.

Add a judgment condition, if the file is pdf or docx and the size exceeds 50kb, the attachment will be saved.
You can modify it according to your actual needs

Expression:
div(items('Apply_to_each')?['Size'],1024)


Save and test the flow.
When I receive an email like below.

After flow runs, test7.8-1 will be created in my Google Drive.

Hope the content above may help you.
Best Regards
If my answer helps, then please consider Accept it as the solution to help the other members find it more quickly.