The potato machines with 8gb of RAM is a luxury! Most old machines that I can get my hands on are 2 or 4 gb of RAM!
The most lightweight that I try recently was antix, but my daughter couldn't get the feeling. So we went with MXlinux and was really good. She plays Harry Potter 1 on wine and is really happy!

The "old laptops" mentioned are newer than my still in use laptop (Ivy Bridge i5 with 8GB of RAM). I really don't think a guide is necessary for this level of hardware, just slap any decent distro and play lightweight stuff (including most things from before 2010, including big games like XCOM: Enemy Unknown or Dragon Age: Origins).

Haswell processors (~2013) already had partial Vulkan support and everything. A guide might help with debugging eventual problems (i.e., try to run Proton games with PROTON_USE_WINED3D = 1 if it doesn't work at first) but that is not even mentioned.

Except for Vulkan support, anything in the Core i3/i5/i7 series should be pretty much the same as modern Linux provided you have enough RAM (with 4GB or less definitely look into Lubuntu or lighter). It gets difficult only when you move further back - when you might not have a 64 bit CPU, or have <1GB of RAM or, trouble with OpenGL 3.6 support, or dedicated graphics might not even support 720p video properly, etc.

So we went with MXlinux and was really good. She plays Harry Potter 1 on wine and is really happy!

Nice!