There is a specific issue around Big Sur and the response from the developer in regard to this is.
I've been using Big Sur since the week that the first developer beta arrived without any problems. This particular issue seems related to the setting in the System Preferences, General section, to "Prefer tabs [always] when opening documents". If you change "always" to never or "in full screen" then it's not an issue. I've got a code workaround in mind that should fix this in the next preview, but in the meantime I recommend changing that system setting. Otherwise, Big Sur is quite stable and if you don't mind some of the system's UI choices I do recommend it."
This is a MacOS System setting, not a Moneydance setting.
As far as native support is concerned it is dependent on a native version of Java becoming available for this operating system/processor combination. The developer has said he will build native version of Moneydance once this is available.