how should I format an external SSD to install sequoia??

I had my MacOS running from an SSD, last day I was trying to update Sequoia but something went wrong and now the external SSD is not booting anymore. I have tried several things but nothing worked and now I have to format again the external SSD: I did this procedure years ago with Catilina and then I always kept the system updated. Now, if i download Sequoia, the external SSD is not showing as a suitable device for installation, and if I connect the external SSD the OS says that it is not compatible with the system, even if i can read and access the files Can someone tell me how should I format the SSD to install Sequoia?? I already did the backup... thanks a lot!!