XAMPP SSL Tutorial https://shellcreeper.com/?p=2573

make-cert.bat

@echo off
set /p domain="Enter Domain: "
set OPENSSL_CONF=../conf/openssl.cnf

if not exist .\%domain% mkdir .\%domain%

set dir="%cd%"
cd ..\php
..\php\extras\openssl\openssl.exe req -config %dir%\cert.conf -new -sha256 -newkey rsa:2048 -nodes -keyout %dir%\%domain%\server.key -x509 -days 365 -out %dir%\%domain%\server.crt

echo.
echo -----
echo The certificate was provided.
echo.
pause

Updated for current XAMPP 3.2.4 (2020/8/2) file layout.

Note: I also had to provide the full path to the files in the crt directory when creating the VirtualHost directive's SSLCertificateFile and SSLCertificateKeyFile values.

Thank you @airways, it helped :) 💯

where to put the file. my xampp in D:\xampp

This script is updated based on the article here, which gives all the other information for the process:
https://shellcreeper.com/how-to-create-valid-ssl-in-localhost-for-xampp/