Hopefully the same will be true for third party apps.
If the number of new updates on MacUpdate is any indication (as it usually is when an OS upgrade is issued), it already has.
Yeah, the number of updates there have been increasing, but possibly not all of them are for Big Sur compatibility. For example, there was an update for Thunderbird earlier today (I use it), but still no indication that it is compatible with Big Sur (yet). Probably a little to early.