I still run 5.5.x on an old Win2012 server box. I like to upgrade to 6 and have a couple of questions:
1.) will BlueIris still work on a Win2012 sever?
2.) Does v6.x require more system resources than 5.5?
3.) what is the cheapest way to upgrade?
I see no reason that it would not work if V5 is running fine, there is a C++ library that it needs and should download automatically so hopefully you have internet access on the BI system, If you are going to run the built in AI then it will consume more memory and CPU, if you have a current support contract the cost to upgrade is "$0" if not then you can purchase the support agreement depending on the version of BI5 you are running it might be better to upgrade then renew your support as the support payment processor in older version no longer works!
I have no idea; you could download an evaluation and try it! Does the 2019 server have a desktop experience add on, which it would probably need for the software to interact with the user, I have never used Server 2019, I retired from my computer job 25 years ago!