Some apps can/will detect that an OS-level VPN has been activated though, and refuse to work at all. Spectrum TV does this for example, as well as some banking and other types of apps.
Yes and sites can also fairly reliably detect when a user is coming from a well known IP address block belonging to a VPN or VPS provider. It’s a built in feature of I know at least AWS
Assuming you are using a "well known IP address block belonging to a VPN or VPS provider", yes, but it is also possible to setup VPNs/proxies outside of well-known IP blocks.