When you post on reddit, instagram etc. you're giving the company your valuable data. (And it often is valuable, you put your thoughts into it and all that). Consider if you take 15 minutes to create value content, you'd get paid $5 or sth if you were doing it commercially. Now all that value is donated to big tech companies. (that's the only reason why they have value at all.)
So what's the problem with that? The problem is that reddit and others can instantaneously put your years-long effort behind a paywall. I'm not joking. Look at these:
when i want to see content on reddit (for research) or instagram (for local community) they don't allow me to see the data that users have contributed. Reddit claims that it blocks VPNs for "security reasons", meanwhile i'm using VPNs in browser's incognito mode to not be tracked. Instagram wants you to sign in sothat they amass more users and can take leverage of the network effect even more.
I can understand restricting who can post to limit bot activity, but reading must always be possible. After all, it's our data. That's exactly what happens when you give your data to big companies to "communicate with other people": your data becomes a source of income for them, at our expense.
VPNs prevent the site from attaching an IP address to the site visit, and incognito mode means that browser cookies routinely get scrapped.
While this is a popular selling point that VPN providers like to advertise, it's pretty misleading in terms of what this actually means with regards to tracking. Realistically, this does almost nothing to prevent sites from tracking you. They don't see you at your home IP as "John Smith" and see you on your VPN as "Hans Schneider", instead they see you at your home IP as "John Smith" and on your VPN as "still John Smith, but either traveling in Germany or using a European VPN".
Advertisers have tens of thousands of individual data points on nearly every single person who uses the internet at all for any purpose. All a VPN does is obfuscate ONE data point. That's less than 1% effectiveness at hiding your identity from advertisers. A VPN does basically nothing against all the other fingerprinting methods advertisers have.
Think of using a VPN like speaking into a walkie-talkie: your voice comes out at a different location, but if the person on the other end already knows what your voice sounds like, then they still know who you are, just not necessarily where you are. Unless you're taking other efforts to mask your voice, the walkie-talkie isn't protecting your identity in any way. Likewise with a VPN, if you go to the same sites from the same devices and log into the same accounts and otherwise engage in the same online behavior, the VPN is only hiding where you are, but it's still trivially easy for an advertiser to determine who you are.
This is a bit of a pet peeve of mine, because VPN providers harp on this idea so hard in their advertisements that it tricks people into thinking VPNs are capable of things that they just simply are not.
A few browser extensions can help with that further. UBlockOrigin, NoScripts, CanvasBlocker, Privacy Badger, Consent-O-Matic, etc. Maybe Decentraleyes but I don't fully understand that one yet.
Then there's DNS proxying and/or DoH, and a variety of other settings that can be tweaked for maximum privacy.
Any one of these things alone will leave holes, but putting them all together can significantly reduce your trackability and fingerprint. Of course it's a trade-off because some of these will break websites, but most allow granular exceptions so you can still use the sites you need.
In any case, a VPN is an important part of that, but the main purpose is to make it harder for your ISP to track you. Obscuring your IP from web hosts is just a bonus.
https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/
Firefox Multi-Account Containers lets you keep parts of your online life separated into color-coded tabs. Cookies are separated by container, allowing you to use the web with multiple accounts and integrate Mozilla VPN for an extra layer of privacy.