create simple SHA256 key + CSR

openssl req -nodes -newkey rsa:2048 -sha256 -keyout test.key -out test.csr

create key + CSR from config

openssl req -new -config test.conf -keyout test.key -out test.csr

config file example

[ req ]
default_bits = 2048
prompt = no
encrypt_key = no
default_md = sha256
distinguished_name = dn

[ dn ]
CN = subdomain.example.com
O  = MyCompany
OU = oranizational unit
L  = location
ST = state
C  = country

config file example with SAN

[ req ]
default_bits = 2048
prompt = no
encrypt_key = no
default_md = sha256
req_extensions = req_ext
distinguished_name = dn

[ dn ]
CN = subdomain.example.com
O  = MyCompany
OU = oranizational unit
L  = location
ST = state
C  = country

[ req_ext ]
subjectAltName = DNS: subdomain.example.com