This is a complicated scenario but I try to make the problem simple.
I did not use SharePoint's own approval process, but added an Approver view through InfoPath and then cooperated with SharePoint Designer to complete the complex approval flow required by the client.
At one of the approval levels, there are multiple managers and only one manager is required for approval. If he rejects, the entire application will be rejected and will not be sent to next approval level. These managers receive the approval e-mail at the same time. So there is a problem. When multiple managers approve at the same time, one manager approves it when another rejects it.
So I want to add a mutex to the form. When a manager approves, other managers can't approve it. But I can't add a mutex to Form Load rule because the rules added here also run when someone displays the form, causing the form to be locked so others can't browse or approve it.