Changing OS for the first time is scary, but there are ways to try them without risk (specially linux).
Even though there are better communities for this, like lemmy.world/c/[email protected], I’ll try to help a little. I would recommend creating a virtual machine (in Windows probably VM Ware would be easiest). There you can install any OS you want and it’s isolated from anything else on the PC. Try the programs you want or need, but bear in mind than installation is different than in Windows. In Linux software is installed from repositories managed by the distro and almost all distros offer a graphical interface for this (like Play Store in Android or App Store in iOS). I may add that you can create a bootable USB and start the system from there. That lets you try the OS without install and anything you do there will reset the next time you boot from the USB.
Regarding choosing the perfect OS the first time, don’t even think about it. In reality it doesn’t really matter. There’s a thing called distro hopping and is exactly changing distros frequently, many Linux users do it and it’s totally fine to find a better distro for you down the road. Find one with a large userbase, like Fedora or Ubuntu. If you like gaming I would recommend PopOS (based on ubuntu) or Nobara (based on Fedora), so pretty much any issue you have can be looked up on the OS they are based on. This gives you access to a large group of people with the same issues or maybe they already solved it.
Having an old PC you are probably better off with Linux than with Windows. Linux is pretty famous for not consuming many resources and the support for older hardware is incredibly good.
One thing I should say is the different desktop environments. There are a lot on Linux. Find the one you like most, it’s that simple. The biggest ones are Gnome and KDE. They have great support and most distros have installs with one or the other to let you download and install the one you want.
I hope this helps you somehow and even though I don’t think the initial fear is going to go away for a while, I would like for you to give it a try. It’s really liberating not having ads in your OS or being profiled by it.