ラズパイ4をUSBブート出来るようにすることは可能なのでしょうか？
公式にはサポートされていないと聞きましたが、出来れば、SSDのみで起動させたいと考えております。

詳しくお教えいただければ幸いです。

In my case. I used 64GB and 128GB USB memory, but both were bad.

I tried it with another USB memory (new). However, the same error occurred and I could not copy. If so, is it a problem with the main unit? ?
Please tell me how to solve it.

I have the same problem.
I reworked the physical format, but no matter how many times I do it, the word "COULD NOT MOUNT PARTITION" appears and the work stops. Is this device (USB memory) no longer available?