I have my iPhone 13 Pro Max for 4 years now and the only problem I really have is storage and the battery.

I'm debating if I just replace the battery and let this run another year... since the iPhone X I haven't seen any major upgrades still that feel like they'll matter in my day-to-day life.

A flip would be different...

I'm still rocking a four year-old Note 20 Ultra. I bought it new the week after they announced the Note 21 Ultra when it was clear they were dropping expandable storage. So it's five year-old tech and I can't see any compelling reason to upgrade. It still looks practically new despite never using a case and dropping it dozens of times. It runs all the apps I use quite fast and there's nothing slow about it.

I keep looking at new flagship launches and I keep not seeing any new capability, feature or performance that would make a noticeable difference to me. I replaced the battery myself last year and generally keep the OS clean, not letting app cruft accrue. I'm not a luddite nor am I price sensitive. I remain ready and willing to buy a high-end flagship phone the moment it does anything new I actually care about. It still gets regular security updates even though a couple years ago Samsung stopped updating it to their latest customized version of Android. And despite looking, I still haven't seen any new Android OS or Samsung One UI feature that would matter to me. Bottom line: I don't think it's you or me, I think it's that phones are mature tech and unless you have a specific use case or it breaks, there's just not much reason to upgrade.

Definitely replace the battery, it will make a huge difference in your everyday use.

can't you get 1tb?