I'll be honest, creating a Facebook account puts your privacy at risk no matter what device you are using. If you want to be as safe as possible, create the account using a burner email, burner phone (if they require phone number; haven't used Facebook in years so I don't know the current climate with it), fake name, and falsify the other personal details about yourself. To enhance your privacy, use a trustworthy VPN in a security-hardened browser like Librewolf (with Ublock Origin ad blocker installed and all filters enabled) on a security focused Linux distro like TailsOS (don't use TOR, it's a CIA honeypot) on a libre-booted ThinkPad (The T400 or X200 would work quite nicely and are cheap).

But to answer your original question, buying a used laptop will not inherently help protect your information. In fact, if you use an OS that the previous owner installed or used, you could run the risk of being compromised by viruses or rootkits leftover from their use. That's why I always do a fresh install of the OS when I buy used laptops (and I do buy a lot, I have a ThinkPad addiction ). Heck, it's a good idea to do a clean install even with a new computer.

You could create a virtual machine, for example, using VirtualBox or something similar.

That's a great suggestion! I've used VMs before for situations needing more safety and security, like testing software that I don't trust.

If you must, a laptop could be purchased with cash from a pawn shop, preferably from out of town.  I'd say replace the hard drive but running a DOD standard wipe and a luks encrypted linux distro should do the trick.  Just make sure it randomizes the MAC addresses of your network interfaces.  Tails and Kali should do this by default.  Other than that, run with the previous posters' recommendations and definitely use a VPN purchased anonymously.  You can't maintain anonymity if the breadcrumbs can be followed (billing information, contact information, IP/MAC addresses). They all lead back to personal identifiable information and ultimately your physical address.

If you must, a laptop could be purchased with cash from a pawn shop, preferably from out of town.  I'd say replace the hard drive but running a DOD standard wipe and a luks encrypted linux distro should do the trick.  Just make sure it randomizes the MAC addresses of your network interfaces.  Tails and Kali should do this by default.  Other than that, run with the previous posters' recommendations and definitely use a VPN purchased anonymously.  You can't maintain anonymity if the breadcrumbs can be followed (billing information, contact information, IP/MAC addresses). They all lead back to personal identifiable information and ultimately your physical address.

Running Linux will make you more visible actually.