Some people told me not to update the most recent MacOS due to bugs, compatibility of apps, unstable OS, and more but to update every 2 years.
Other guy said that he needed to update for the newest MacOS cause Adobe programs always update base on the recent OS.
Any thoughts about the annual updates for MacOS so far? Would it be a stupid idea if I update MacOS 1~2 years later?
An operating system is essentially a big complicated program that lets multiple other big complicated programs live in relative harmony on the same system. Sure, there are features in any given operating systems, but the key drivers are all of the other programs you use.
This is why some say that video production houses, professional musicians, etc. should be cautious about upgrading to the latest OS, since multiple things can break.
The advantages/disadvantages of upgrading your OS are highly dependent on what you do with your system, what programs you rely on. If you aren't running those Adobe programs like that other guy, well, you don't need to worry about those, but you do need to be concerned about the programs you do rely upon (none of which you bothered to mention).
The biggest problem with staying behind is that third-party software developers will eventually obsolete older versions of the operating system by no longer making new features available to those systems running the older OS.
Ideally, if you are reliant on a certain set of applications, you upgrade the OS to the latest version on a secondary boot drive as well as all of the applications. If it doesn't work, you resume booting off from your normal boot drive. Upgrade the secondary boot drive on a regular basis to see if problems have been fixed. When a new major update of the OS comes out, get another secondary boot drive and continue the process.
This may lead you to have multiple boot drives, each with different software package versions from different eras, all more or less matches to the OS of the time.
Do I keep an archival boot drive for every major macOS release? (10.12, 10.11, 10.10, 10.9, etc.) No, I do not. But I do have a 10.6 Snow Leopard boot drive (the original version for my 2010 vintage Mac mini) and another boot drive from a few years ago (probably Mavericks). The 10.6 Snow Leopard drive has the last supported version of the iLife apps available for that era. The Mavericks boot drive has the same, plus iWork apps. Oddly, this drive is more of a pain to run these days since much of the Apple cloud services have changed, so there are incompatibility issues between an older, slightly cloud aware version of the macOS (former OS X) and today's iCloud services. By contrast, the Snow Leopard boot drive is basically blissfully unaware of the cloud.
Especially with the advent of the App Store, you really need to update the apps to the current version as supported by your OS. Eventually, the older versions are pulled and if you are running a boot drive with an older OS, you often cannot update your apps to the last supported version for that particular OS.
Meaning, if I built a brand-new Snow Leopard boot drive today for my venerable Mac mini, most of the apps I would want I wouldn't be able to find. Sure, it would run fine with the basic pre-installed apps and I could probably source the last Combo Update for the OS, but in some cases, it would be nearly impossible to find the last/best version of other programs for that specific OS. By having retained a secondary external Snow Leopard boot drive from circa 2008 (or so), I have a snapshot in history. My 10.6 Snow Leopard boot drive has copies of Final Cut Express, LiveType, iPhotos, the old iMovie HD, iDVD, and iWeb. I can't buy a copy of the last version of Final Cut Express today.
By making OS upgrades free, Apple has removed the primary barrier for Joe Consumer to update to the latest and greatest version of the OS. This means that third-party developers have fewer systems running older OS versions to support which leads to them to stop supporting those older OSes rather quickly (unlike Windows developers who are compelled to support large numbers of systems running legacy OSes).
In summary, there is nothing wrong with running a macOS that is running 1-2 years behind the current version, but you want to keep up with updates on a secondary boot drive simply because if you are running a 4-year-old OS and want to upgrade to something that is 2-years-old, you probably won't find the matching applications based on the way that Apple and third-party developers sunset discontinued versions of their apps.
Good luck.