it is not possible to be 100% anonymous on the internet

This is a dumb thing people repeat because they see other people saying it.

You don't need to worry about your IP if you buy Walmart gift cards with cash (or pay a homeless guy to buy them for you), and with those buy a VPN that doesn't keep logs and doesn't cooperate with police (like PIA), and enable the kill switch when you're using it so your real IP is never revealed. You now have an IP that can't possibly be traced back to you.

You can take this a step further by buying a laptop with cash, running TAILs/Whonix/etc. on it with Tor over VPN.

The only issue now is what you say online. If you can't use the internet without exposing yourself, that's your fault and doesn't let you say "it is not possible to be 100% anonymous on the internet". It's possible, you just chose not to.