For what it's worth, we announced that Flash Player was EOL back in 2017, before you bought the projector. I suspect that had a lot to do with why you got such a good deal on it. There's an aphorism in computer science: "Change is the only constant". There's no such thing as "write once, run forever", but part of the reason that hardware includes updatable firmware is to manage that change without wasting hardware. It's still up to the vendor to provide that support, and/or have the right financial incentives to do so.
Anyway, here's the original announcement from 2017:
https://theblog.adobe.com/adobe-flash-update/
You *do* have the option to use Enterprise Enablement, but it's non-trivial.
We didn't do this in a vacuum. All of the browser developers are simultaneously dropping support for browser plug-ins. Safari, Firefox and Chrome have all dropped plugin support at this point. IE and Edge aren't too far behind.
The reality is that browser plug-ins really needed to go away for the web to move forward from a security perspective, and because Flash Player's footprint is roughly a couple billion active installations, on machines largely owned by non-technical people, we had an obligation to put them in a secure-by-default state.
Now that the generally available Flash Player shipped by Adobe is no longer maintained, it's a matter of time before the malware/ransomware scene develops an exploit. Limiting Flash Player's behavior to loading only explicitly allowed content minimizes the risk that the average user is going to encounter a malicious banner ad that leads to their machine being compromised. This is important for the health of the ecosystem at large.
So, you'd really need to make a dedicated, air-gapped machine for managing the projector. You'd need a copy of Flash Player and the latest Firefox ESR, which then never get updated. You would configure Flash to load the necessary content from the projector using the Enterprise Enablement features, and you'd discover what that content is by using the related logging features. Once you get it working, this configuration would absolutely not be suitable for browsing the web with, and you would want to think about how to best prevent that from happening.
You can read more about Enterprise Enablement on pp.28 of the Flash Player administrator's guide:
https://www.adobe.com/devnet/flashplayer/articles/flash_player_admin_guide.html
Your organization also has the option to license a maintained copy of Flash Player moving forward, from our support partner HARMAN; however, replacing the projector would be far more cost-effective.
You can read more about enterprise options for Flash Player, here:
https://www.adobe.com/products/flashplayer/enterprise-end-of-life.html
Good luck!
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