ISP can’t see pages. They can see domains or IPS but that’s it.
I use incognito so I can sign into multiple accounts on the same websites at once.
Firefox containers is your friend. It’s way better. I can sign into dozens of separate pages for different clients in a single browser window in different tabs if I want.
Incognito is only good for one reason: Not having those sites in the browsing history.
I use it to get around website article limits when they try to force me to sign up.
Websites with actual web devs block and track usage with ip instead of cookies/cache, nothing a vpn can’t stop tho. More reliable to is to the way back machine on archive.org. Can also use a browsers reader mode to get around it too sometimes.
It’s good for using someone else’s computer without having to worry about passwords being saved or making sure you logged out before leaving