I have this laptop from like 2012 that I use a lot and I can even say it's my main Linux machine. It's got 8 Gb of RAM and a dedicated GPU so it's not bad but it has an HDD so slow it takes what seems to be 30-60 seconds to launch a web browser. I guess it's 5400 RPM. I want to finally buy an SSD for the machine.
However I noticed that all of the brand new ones that are available in my area are either SATA3 (for SATA) or PCIe 3/4 (for M.2). The laptop obviously supports none of these standards.
Will such an SSD work or do I have to search for a used one with an older standard (like SATA2)? Adapters might be a problem to get because I'm not a customer of marketplaces I can get them from so I'm afraid of getting scammed or just not figuring out the purchase procedure.
Should be fine, SATA3 is backwards compatible AFAIK. If the laptop can take a 2.5 inch SATA drive then you should be okay.
I happen to have an even older laptop than yours (from 2008 era) that's been rocking a 2.5 inch SATA SSD for at least 5-10+ years now. Works fine and was definitely an improvement over the old performance. The laptop is still quite old/slow in other ways but that's expected from something that old.. luckily it's not my main computing device.