I probably wouldn't go as far as never buying anything online, but paying cash IRL should be something done by everyone to protect their privacy. There are a few other easy things that can massively improve your privacy with minor or no inconvenience: Linux on every PC/laptop, GrapheneOS on phone(s), uBlock on every browser (or a DNS-level sanitizer), car without cellular modem (pull the fuse), non-Google and non-Apple email (ideally your own server or a small provider in a friendly jurisdiction). Also, don't use social media and text over Signal instead. Of course, TVs and other home appliances should be kept off the Internet. Overall, those are some very minor sacrifices for anyone with a little bit of maturity. It's very far from living off the grid or anything like that.
That's a very early 2000s view of the issue. Ads are not what all the surveillance is for, it's just the publicly acceptable excuse for tracking you that companies love to use because nobody cares which ad they get shown. Being able to build a profile of which websites you visit can provide a ton of information about you and that data is increasingly being used offline. It stopped being about ads ages ago and now what you do online can impact your next job offer, what prices you pay, which policies companies apply to you, etc.
You can never limit all data collection. Going to the store and paying in cash will still have you tracked by Flock cameras. The point is just to limit what you can, where you can. Every scrap of data collected about you is going to eventually be used against you later by somebody. No point in giving them anymore ammo than you have to.