Don't consider at all: All non-OEM Chinese stuff (1 trillion brands, way too many to list, including the usual consumer garbage that you might find in a store like Reolink etc.)
Consider if cost turns out to be a factor: The two major Chinese OEMs, Hikvision and Dahua.
Note: All Chinese OEMs are obviously implicated in the Chinese surveillance state. Obviously. A lot of "major" brands are OEMed by these two, even ones you might not expect. For example, much of Panasonic stuff is rebadged Dahua. Basically 90% of any CCTV camera Made in China comes from either Dahua or Hik, the lesser brands just mostly get (or rather, choose) the bargain-bin hardware with monkey-model firmware and of course no FW updates ever.
If cost really isn't a factor: Bosch, Axis, Dallmeier, Mobotix
Note: Most of these you cannot buy directly, and the vendor won't talk to you.
> What’s the best, in terms of open source support and reliability?
These are found at completely opposite ends of the spectrum. All good CCTVs cameras use signed and more-or-less well encrypted firmware, even cross-flashing isn't much of a thing.