I have an HP computer I've bought in 2009 and it runs Windows 10 flawlessly.
Maybe it is depends on the hardware then. My 7 years old HP Desktop takes about 20 minutes to boot Windows 10 and my 5 years old Toshiba laptop (that no longer getting Windows updates since this year January) also takes about 15 minutes to boot. Running the OS is actually not the problem but the boot time takes ages and launching apps for the first time can also take ages so if I have only 10-30 minutes to jump in and do something, it was getting on my nerves lately.
Now it could be the AV I`m running, so I have uninstalled my AV few month ago and was sticking with Windows Defender for a bit but did not improved anything and after getting a malware infection I decided ok, time to go back to a proper AV.
I also tried cleaning the system with CCleaner and defragmenting the hard drive and ssd, did improve a little but not significantly.
Did also check autostart apps, disabled everything but nothing.
Judging from the system monitor it was mostly Windows processes eating all my CPU and Storage resources, often running the CPU at 100% and also reading and writing the hdd and ssd at 100% at boot time and it was killing me. But for me it was always like this with Windows.
Linux is the best, it is not slowing down, it is just break instantly and decide one day not to boot or not to update ever again and apps not to launch because of broken dependencies, Ubuntu 12.04 was the last version that worked for me I was using it for 4 years but since 16.04 not a single Linux distro last longer than few months for me, the last one I tried was Pop!_OS 18.04, I was using it for about 8 months, but after the boot time did increase and took about 5 minutes to get to the login screen and after an other 4-5 minutes to launch an app but in this case it was a known bug and the only solution was is to do a fresh install. Don't know if they have fixed it.
Maybe I am just not lucky but honestly I can not complain about macOS and iOS slowing down over years, it does feel natural to me but I understand the experience can be different for people.
still not sure what to do for the best.
Honestly, if you really want to give iOS dev a try, consider switching to macOS completely and get a more recent hardware.
I was also struggling with this for almost 10 years because of Windows software I was using, because of the price of the hardware, because of the low specs of the Mac compered to PC at same price point and negative feedbacks from people.. but finally I got my 2019 iMac 1 month ago, so I don't have a lot of experience but I am totally happy with my purchase so far. macOS is nice, takes some time to get used to but since I was a big fan of the Gnome desktop on Linux, I do like the overall look and feel and the way it functions not the same as Gnome but similar. Many free and open-source software is also available for macOS and works nicely, also many game engines if you play around with multiple engines like I do but if we consider AAA ones only, there is Unity, Unreal and GameMaker, and lots of Indie engines like Cerberus and also SpriteKit, Apples own game framework which I did give it a try and it is pretty neat to be honest, does have some good points but obviously it is not cross-platform so it is not for everyone. If you develop cross-platform apps there is also Xamarin, Slutter, React..etc So there is not a lot to lose from developer point of view by switching to macOS.
The only thing that bothers me about macOS is that, Inkscape runs horrible for some reason, it is so slow takes 2 minutes to redraw a circle when I resize it, I have no choice but to consider to get a paid one, I am looking at
Affinity Designer, looks nice.
Also games runs horrible, even if on paper the Mac have the specs, games are absolutely not been optimised for macOS and does not run at all. The iMac I have on paper have much better specs than my Windows desktop but still can not run games much better, some games even runs worst. At first I was extremely disappointed but then I thought "challenge accepted", sure I can make games runs better than this. I did some tests with different engines and frameworks and yeah, I see no reason for those games running so bad and can be done better. In-fact I think most of those games was built using old versions of Unity and Unreal but if the devs care to port the games over to the latest version of those engines and rebuild, it could improve things significantly without lot of work required, but as I have realised most Indie developer just simply hate Apple and macOS and don't bother and big studios looking at it strictly from financial point of view and obviously it doesn't worth it for them to take a 5 years old game and rebuild it using new, better version of the engine just to run better. But games using an in-house engine runs fine, It is mostly Unity and Unreal engine games from 5 years ago that runs horrible.
So if you play AAA games a lot it can be a very though decision, macOS is not for games, not because it doesn't have games but because games don't run on macOS.
If you don't actually play AAA titles that much only casual games maybe, and you don't currently use any Windows only software then I can totally recommend to consider switching to macOS and get a more recent hardware.
However, I can not really comment on how long Apple going to support the current Intel Macs but I expect them to support it as long at least the AppleCare+ cover last since it does cover accidental damage up to 2 times I believe. It is indeed uncertain times to get an Intel Mac of any gen but if you do I recommend getting a more recent to replace Windows if you can.