Yes, you can add students manually via Admin > Students > Add Student Manually.
Just enter the information as required in the correct fields, and when you're all done, click the orange Add Student button.
Note: Fields relating to COVID-19 are especially important to fill out correctly, as they feed into the statistics collected every day by the DfE.
This is a handy way of creating a placeholder entry for students when you're waiting for CTFs to arrive, as you can always return to the profile to edit/update details at any time (for example, if you don't have a UPN for the student when you create the profile, you can allocate a temporary one and then add their real one later).
TIP: Once the student's official CTF arrives, you will have the option to merge the CTF with the profile you have already created.
For more information see: Using the Full ATF/CTF Importer