It's 2023.  Let me get this straight...

Flash content no longer runs in any modern browser.  There's a WIP in-browser flash emulator/player written in rust that aims to correctly and safely run flash content, but it's incomplete.

Unity has continued to bloat the engine in addition to making some..."interesting" decisions about pricing fees, contracts with defense agencies, and uh...laughable PR announcements, to say the least.

Godot Engine has recently launched a new major version, Godot 4.  Godot 4's HTML5 exports currently can't yet run on macOS and iOS due to upstream bugs with SharedArrayBuffer and WebGL 2.0.

Godot 3 builds can be exported as threaded builds to help with allowing lower audio latency (among other things), but this requires SharedArrayBuffer support, which in turn requires some COEP web headers to be served, so you need to configure your webserver to provide those (it also doesn't work on Internet Explorer, but let's be real, nobody cares).

If you're hosting on itch.io (as many do), there's now an experimental flag you can enable for your project to have those COEP headers served.  However, they determined that using the "require-corp" version of the header breaks the rest of the page, so they're opting to use "credentialless" instead.  Firefox recently launched trial support of this header, but Safari only accepts "require-corp", so your build won't work there.

...yeah, ok.