I have figured out how to make it work.

Important things to keep in mind:

• Path to SSL certificate must be authorized to the www user
• Configuration must be correct in appSettings.Production.json

To avoid further errors, I've copied the SSL files to another folder

• Ran the command sudo cp /www/server/panel/vhost/cert/site.com/* /www/cert/splatdev.com
• Ran the command sudo chown www:www -R /www/cert/site.com/*
• Restarted the umbraco (kestrel) service

Here's an example of working appSettings file:

    {
      "$schema": "appsettings-schema.json",
      "Serilog": {
        "MinimumLevel": {
          "Default": "Information"
        },
        "WriteTo": [
          {
            "Name": "Async",
            "Args": {
              "configure": [
                {
                  "Name": "Console"
                }
              ]
            }
          }
        ]
      },
      "https_port": 5001,
      "AllowedHosts": "*",
      "Umbraco": {
        "CMS": {
          "WebRouting": {
            "UmbracoApplicationUrl": "https://www.site.com"
          },
          "MacroErrors": "Silent",
          "ModelsBuilder": {
            "ModelsMode": "Nothing",
            "DebugLevel": 0
          },
          "Global": {
            "UseHttps": true,
            "Smtp": {
              "From": "noreply@email.com",
              "Host": "smtp.server.org",
              "Port": 587,
              "Username": "postmaster@site.com",
              "Password": "xxxx"
            }
          },
          "Content": {
            "Notifications": {
              "Email": "admin@site.com"
            },
            "Error404Collection": [
              {
                "Culture": "default",
                "ContentKey": "5f7d140d-871d-4133-bc89-b899c69685f0"
              }
            ]
          },
          "Hosting": {
            "Debug": false
          },
          "RuntimeMinification": {
            "UseInMemoryCache": true,
            "CacheBuster": "Version",
            "Version": "112233"
          }
        }
      },
      "ConnectionStrings": {
        "umbracoDbDSN": "Server=localhost;Database=Site.Umbraco.Cms;user id=uuser;password=xxxx",
        "umbracoDbDSN_ProviderName": "Microsoft.Data.SqlClient"
      },
  //to use with mailkit
      "MailSettings": {
        "From": "noreply@site.com",
        "Server": "smtp.server.org",
        "Port": 587,
        "SenderName": "Webmaster",
        "SenderEmail": "webmaster@site.com",
        "UserName": "postmaster@site.com",
        "Password": "xxxx",
        "AdminEmail": "admin@site.com"
      },
      "Kestrel": {
        "Endpoints": {
          "Http": {
            "Url": "http://localhost:5000"
          },
          "HttpsInlineCertFile": {
            "Url": "https://localhost:5001",
            "Certificate": {
              "Path": "/www/cert/site.com/fullchain.pem",
              "KeyPath": "/www/cert/site.com/privkey.pem"
            }
          }
        }
      }
    }

Also, I am using Cloudflare, so I had to add a custom rule to disable X-XSS-Protection

And then, point the reverse proxy rule to port 5001

Now, I got the health checklist to go all green