Before getting your hopes up: Check if your specific phone model is supported by any of them. On lots of phones you can't change the software and you're stuck with the manufacurer's version.
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It's an old Motorola model from several years ago figured I turn it into a more secure second device
Good idea. I think GrapheneOS won't work with that as they're focused on the Google Pixel devices. But you could have a look at the LineageOS compatibility list. Just the manufacturer is a bit unspecific. But you can look up the exact model in that list.
I can't really comment on all of the other Android variants. There are so much of them and I'm not up to date anymore.
Just use Lineage if you can. It's the biggest one with the broadest support.
IF It's a Motorola, there is a big chance Lineage os will support it
It looks like it does, or at least used to
though I made the mistake of asking some advice on Reddit and just got insulted.
LineageOS is your most likely bet. Check the lineage website and see if your specific phone model is supported. LineageOS maintainers are all volunteers so it's hit or miss which devices any of them have chosen to support. If there's no official support someone may have built an unofficial ROM for your phone over on the XDA forums, many times that's the only place to find support. Google "LineageOS XDA yourModelHere" if you don't see your phone on the official list of lineage supported devices.
In the future it's a good idea to check for LineageOS support before buying a phone if Lineage support is one of your priorities.
these days unless you have a very popular Samsung, Oneplus or a Pixel you usually don't have much choice.