Hi @Meeting Room ，
Welcome to our forum.
I have tried to create a flow to save attachment to onedrive on my Power Automate like below, but it could work normally without saving any preview image that you mentioned.
It's suggested to compare your flow with mine to check, as I know, you could also specify which type of attachment that you would like to save via adding specific conditions.
If your flow is actually same with mine and the issue still exists, due to this issue may be more related to Power Automate, please kindly understand here we mainly focus on general issue on Outlook desktop client, we may know little about Power Automate, in order to solve your issue better, it's suggested to post your issue in this Power Automate community
Hope your issue would be resolved soon.
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