In the zip file that you have received for your Sectigo SSL certificate, it will only contain 2 files.
The first file is .crt and the second file is .ca-bundle file.
If you require the SSL to be in the format like der, p7b and pfx, kindly note that you will have to convert it.
There are 2 ways to convert the file.
way is to use OpenSSL by using command below.
.crt to .der:
openssl x509 -outform der -in certificate.pem -out certificate.der
.crt to .p7b:
openssl crl2pkcs7 -nocrl -certfile certificate.cer -out certificate.p7b -certfile CACert.cer
.crt to pfx:
openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt
way is to use a website like https://www.leaderssl.sg/tools/ssl_converter
which you can use to convert the .crt file to the extension that you require.