I find it fascinating how whenever there is a new Apple dog and pony show, everyone decides they need a new computer.
I'm sitting here writing this on a 2010 Mac Pro. Long since EOL'd by Apple. Still running Mojave. Apple's newer machines are the ones you need to worry about in regards to "support". They have a far shorter shelf life than the older machines. They aren't upgradeable, whereas the older ones are. They don't run Windows, the INTEL models do. If anything, you'd be replacing the new M1 Macs sooner than you would have replaced the older INTEL ones... assuming you aren't rich beyond rich and buy a new computer whenever there is a new spec upgrade.
Apple is one of those companies that banks on customer loyalty... you know, the guy that buys Mac just because it's a Mac without question. The same guy that uses the same insurance company for years out of habit, not realizing they have been slowly raising their rates on them because they are so loyal. That is they actually took the time to check out the other guy, they'd realize they'd been fleeced by their insurance company for years.
Apple is no different. You've been paying more and more for Apple products than you should be because you blindly accept their price structure. Blindly accept their transition into 100% non-upgradeable / non-user repairable / forced obsoletion model. Why charge x for this computer when you can get y for it merely because you told them this was a good price? They're laughing all the way to the bank. Really. All because you let them tell you when it is time to buy a new computer.
Auto dealers would love to get you to buy a new car each year... most people realize they don't need one until they really do. With Apple products, you're looking to replace them as soon as you've unboxed it. Apple loves you.
I'd keep your computer until it no longer does what you want it to, not what Apple tells you it needs to do. Sort of like when you transmission dies in your car and you figure it would be cheaper to replace it than to fix it.
There will always be a new Mac coming out... even more so now that they know people will buy a new one just because.