Dear @Pawel Musial,
Welcome to the Q&A Community.
We appreciate you taking the time to share a detailed explanation of the issue. Based on your description, here are some steps to configure the default welcome page view for Document Sets in SharePoint:
Note: Admin access is required to perform these steps
Step 1: Sign in to your SharePoint site > Create a new view.
Step 2: Go to Settings > Library settings > More library settings.
Step 3: Scroll to the Views section and select the view you want to set as default.
Step 4: Check “Make this the default view”, click OK, then reload the page.
You can try these workarounds and update us. If the issue still appears please feel free to let us know and we will keep assisting you. Please know that we truly appreciate your patience and understanding as we strive to support you. We are here to help. Thank you very much for your understanding and cooperation.
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