So Mac's get slower in time?

For the most part, slowdown of any computers over time totally depends on the sort and number of apps that get installed and any associated background processes that they install that slowly eat away at CPU time and also disk access causing normal operation and active app usage to get starved for resources. The biggest offenders are so called "optimizing" and cleaner apps. Also, the vast majority of anti-virus apps tend to simply kill performance out of the gate.

You asked; the number of apps installed can affect performance?

installing a number of apps in itself doesn’t really cause any slow down, unless your running low on disk space. Running low on disk space can cause excess ram to disk swapping. The typical number I use for the system needs “at least” 10% of free space left, but 20% is a better number to plan for.

So if you have plenty of disk space, adding more apps is not typically a problem if you keep the disk space free numbers mentioned above.

With that said, what can also cause an issue is having multiple apps running at the same time. Especially heavy hitters a Final Cut Studio, Motion, Logic Pro Studio, and many other professional graphic editing apps.

The key here is to not have all the apps running at once. If you need them for whatever reason to be all running at the same time.

The things to watch/plan for is;

• the amount of memory onboard (ram) and what’s the free space available
• disk access speed in milliseconds
• read/write speeds for hard disks, or SSD

Obsolescence may be one factor, but hardware "wears out" over time ... so, potentially, yes, your Mac (or any brand computer) will see degraded performance over its useful lifespan. Like people aging, there is nothing you can really do about it.

Updates take up storage space over time, apps become more demanding. It's not a case of your mac getting slower, but the tasks it needs to do getting more intense, causing it to generally run slower, in addition to it getting hotter making it run extra slow.

Yes even if you do all those things.

why? Because newer apps utilizing VR and AR, or the next AI systems. Software pushes hardware in some sense.