@gwaitsi as I had to do this again, and completely forgot how I did this last time, here are the instructions for 2021.
Save the device cert & key generated in pfsense locally
rename the device.crt to root.pem
convert the private key to rsa private key
openssl rsa -in device.key -out device_rsa.key
create a file called ssl_key.pem
a) copy the contents of device.crt into this file from
-----BEGIN CERTIFICATE-----
MIIE2jCCA8KgAwIBAgIBHjAN.......
i1M5xmyTK0cyhwQ==
-----END CERTIFICATE-----
b) copy the contents of device_rsa.key into this file below the certificate from
-----BEGIN RSA PRIVATE KEY-----
MIIE.....
ZBjv7j74PS4P7I=
-----END RSA PRIVATE KEY-----
From the netgear switch "Maintenance", "Update", "HTTP Firmware/File Update" select
"X.509 Public Certificate PEM" and load the root.pem
"X.509 Certificate Private Key PEM" and load the ssl_key.pem
From the netgear switch "Security", "Access", "HTTPS", "Admin Mode" - Enable.