S20_User I don’t know the photo quality of the S20, but generally one of the Pixel’s strong points is the camera.
On the official group (chat, not forum), I had read that the photo quality doesn’t decrease with the Gos camera, but the Pixel camera has many features you might want, both for photos and videos.
The Gos camera app focuses more on privacy and has few features, but it was designed that way on purpose.
It follows the classic philosophy of doing one thing and doing it well: reducing the attack surface with fewer features and focusing on removing metadata and improving privacy.
Gos allows you to revoke an app’s permission to connect to the internet, so you can basically use the Pixel camera without granting any permissions.
You don’t need to give permission for it to access photos, because Gos has a feature that lets you use files within apps without giving them permission.
It’s not called storage scopes, I don’t remember well the feature's name, but it was something like media api.
Regarding whether to use a separate profile or not, it depends on your threat model and your preferences.
One common piece of advice is to use profiles to separate your identities, e.g., profile 1 for personal life, profile 2 for work, and so on.
There are other ways to use profiles, but explaining them all would make the message too long.
In your case, if your threat model isn’t particularly high and you need WhatsApp all the time, both for work and personal life, you can simply have it on the main profile, or in the private space if you want a bit more isolation between apps.
Consider how much you actually need WhatsApp, whether you want or need to always be available, or if you want to avoid it being a distraction, and so on.
I’ll leave a link to the most common Gos community profile setups.
https://seprand.github.io/articles/best-user-profile-setup/
Keep in mind that using WhatsApp on stock Android, compared to WhatsApp on Gos, even on the main profile, is still far better in terms of privacy and security.
Not everyone wants or needs a phone that is too inconvenient. You can experiment with profiles later; the world of privacy is a journey.
You might overdo it at first and then go back to stock, but if you understand and accept the pros and cons of your choice, nobody forbids it to do it at the beginning.
Many people simply use a single profile. That’s why I’d recommend switching to Gos.
If the Pixel 9 camera really doesn’t satisfy you, nothing stops you from using the S20 (if you're not going to sell it) just for the camera, but it depends on whether you always take photos or just during travel/leisure, and so on.