For example, by looking at whether your SIM is roaming, what network it is connected to, what network issued the SIM in any second slot, or any other info that would give away your location.
Any app can determine your approximate location just by the internet. The IP you are assigned by your ISP reveals your local location. However, the same IP can be shared by many around you (in your locality), so they cannot find YOU or identify YOU on that basis.
- Using a VPN almost removes this issue, until a website/app decides to compare time on your device to the time of the location shown by your VPN. This is something they usually don't do but certainly can.
- As the Google CAPTCHA does, if many people are connected to the same VPN, they will have the same IP and there will be a lot of traffic from the same IP at the same time. Not something to worry about when not using Google.
They (some apps) also use SIM card info to know your country. (Like tiktok does)
Apart from these they may use your device info to know your country (if your phone is not a Global variant)
And not to mention the location permissions which gives your exact location. (Android 12/13: you can choose between exact and approximate location)
Upvote if this helped.