As a hobby for some years now, I've been helping friends replace the operating system on their old computer with a fresh install of Linux (it's an open source OS that is pretty similar to the Mac OS underneath the hood). It's a way to subvert the planned obsolescence that's built into so many computers now. The oldest system I rescued was a 2008 MacBook Pro, but I've fixed both Apple and PC devices.
Everyone who I've done this for has expressed that they wished they had done it sooner. You will add years to your computer's life and not have to worry about upgrades killing it (as happens with Macs and PCs). This works best on computers with SSDs, and, for a Mac, I will only work on 2019 and older (Apple changed the chips in 2020 in a way that makes it a lot more complicated and with potential future complications, so I wouldn't want to work on one of those and leave you maybe having a problem in the future). I have worked on newer model PCs with no problem.
If you have an old computer whose operating system is no longer able to be upgraded, or where it's gotten too slow to be usable, your computer might be eligible for a switch to Linux. It's pretty easy to assess, and I'll do it for free. If it works and you want to continue, I will charge you $60. If it doesn't work, then no charge (and I don't need to make any changes to your system to test if it will work, so there's no risk). For the $60 I will wipe your hard drive. If you need data to be removed from your system first--that gets tricky and, while it can be done, the challenge of doing that is unique to each computer I've ever touched, and I charge $1/minute for that work because it is impossible to know how long it will take. Exporting photos from an old Mac can be especially tricky and time-consuming. It's much better if you can just bring a computer that does not have any data on it that you want to keep, i.e., export your data to another hard drive or, best, to the cloud (if you export to hard drive that isn't formatted to work with Linux, then we won't be able to load it back onto your harddrive)