Is my Slingplayer compatible with the new system?

The current SlingPlayer Desktop 5.0.92.dmg client for macOS was last built on 2015-03-26. An almost five-year old Mac application might be 64-bit (or not), and it would be surprising if it did not reference library items that Apple has removed in subsequent operating systems. You can try it, but it is a dinosaur. Slingbox does offer installation instructions that though do not explicitly talk about Catalina, show how to allow you to use it there.

In addition to the download site for Windows and Mac SlingPlayer Desktop apps, the same page has a Watch Now button to set up a streaming SlingBox view into a compatible web browser. It may or may not work with recent versions of Safari in Catalina, or earlier.

Slingplayer won't run on Catalina since it's 32 bit. Sling has no plans to make a 64 bit version, which is ridiculous!

You are welcome.