How do I determine my location when using a portal?

By 'Portal', I think you are talking about connecting to web page, whether with an App or a Browser.

without your granting explicit permission, apps on the web can not determine your exact location DIRECTLY.

But they can get an approximation of your location by looking at the IP address you are 'calling' from.

as an example of what can be learned, you can look at this web page:

https://WhatIsMyIP.com

if using Safari browser, there are some settings, especially:

Prevent cross site tracking

to help you keep your identity more private:

Prevent cross-site tracking in Safari on Mac - Apple Support

Note: Every time you visit a website, it gathers data about your device—such as your system configuration—and uses that data to show you webpages that work well on your device. Some companies use this data to try to uniquely identify your device—known as fingerprinting. To prevent this, whenever you visit a website, Safari presents a simplified version of your system configuration. Your Mac looks more like everyone else’s Mac, which dramatically reduces the ability of trackers to uniquely identify your device.

VPN:

A virtual private network, or VPN, is a private connection over the Internet from a device to a specific network.  VPN technology is widely used in corporate environments. If you need to be "present" on an institutional network, a VPN is a great tool for accomplishing this. It is generally issued and controlled by the institution.

Almost all other uses are a SCAM. There is generally no need for you to have a private (and almost always MUCH slower) connection to a VPN vendor's Network, except to make it easier for them to harvest your data to sell. If you are behind a Router you control or Trust, there is NO security advantage whatsoever in using a VPN. Your connections are already encrypted in most cases.

If VPN vendors just stopped there, it would be bad. But many of these packages also insist on scanning all your files, non-stop, -- nominally looking for viruses, but who knows for sure what data they are harvesting. Their non-stop file reading punishes your computer's performance in the process.

Some also break into your other secure connections so they can be FIRST to examine your data, often leaving your Mac MORE vulnerable to attack.

What VPN service to use?

DON'T use VPN services

https://gist.github.com/joepie91/5a9909939e6ce7d09e29

VPN: What you need to know - Apple Community

I have no choice but to use a portal to give the insurance co. the info they need from me on a daily basis. I just wanted to know if there is a way to determine my location when using their portal.