Temporary SSL certificates are simply Self-Signed certificates. It is not possible to create these in the panel, however there are two instances when you will see them displayed in your panel.
If you previously added a Self-Signed certificate in the panel
If you had added a Self-Signed certificate to your domain in the past, it will continue to function. However the SSL/TLS Certificates page now displays it as a 'Temporary' certificate. For example:
If you'd like to change this to a Let's Encrypt or Sectigo certificate, view the following article:
If you are in the process of adding a Sectigo certificate
View the following article for instructions on how to add a Sectigo certificate.
After its been purchased, the panel automatically installs it. During this process, a temporary certificate is set up.
When the Sectigo certificate is finally installed, it takes the place of this temporary certificate.