WebGL player error: "Uncaught SyntaxError: private fields aren't valid in this context" - results in blank screen

I recently set up my own domain to host my Unity browser game. I have the HTML element with the game in an iframe, but once I got it to connect to the file path I get a blank white screen. When I open the developer console it's throwing 1 red error: "Uncaught SyntaxError: private fields aren't valid in this context" for the following line: #if MEMORY_FILENAME. It seems to have a problem with the #if statement. I deleted those 3 lines, and it threw the same error on the #if SYMBOLS_FILENAME line. I can't find anything about this anywhere online. Does anyone have a solution I can try? I'm very inexperienced with this stuff so I have no clue where to go from here. Thank you.