Navigating OpenSSL can be tricky with a number of command line chains to memorise, that generate different products.
Should a temporary self-sign be needed for a website initial deployment or test process, the following webpage has a all in one generator and presents all results on the page itself with nothing needed to install
Only thing of note is industry now requires 1YR max SSL validitty. Some generators will mark the validity for 10 YEARS and RackCorp portal will recognise this as it is technically legitimate.
This webpage generator says 1YR but will generate 3 months, typical of a free self sign 'R3' type generator