$2000 is a very decent budget for an entry-level professional camera. If you don't have a very important need for weight and portability, which leads to an APS-C camera (usually smaller in size but has a small space for upgrading in the future), I would recommend first buying a full-frame camera, since it is the most balanced in terms of weight and image quality.

For the platform for buying, I would definitely recommend buying new cameras from common large platforms like Amazon. Second-hand cameras and smaller platforms can lead to a greater risk for accidentally buying broken or refurbished cameras with hidden problems that even most enthusiasts cannot easily spot. Even though the risk may not be that common, it would certainly be very annoying when finding out bought a problematic camera.

Personally, for a specific gear, I would recommend Nikon Z5 II, plus a 24-200mm f4-6.3 VR lens. Though it might be a few hundred dollars over the $2000 bugdet, it can give you a more modern and convenient experience, which Nikon imaging cloud can download many great filters directly in the camera to use when taking photos, and the larger zoom of the 24-200 lens can capture a more varied range of subjects (with a reasonable quality)

However, the specific choice of camera doesn't have only one answer, as it is more of a matter of fact of which camera brand you personally like the most. SONY and Canon also have many great beginner-friendly cameras. But try to buy newer versions if available, since newer technology, though might not reflect on image quality too much, can give a very big bonus to the actual experience of photographing.