OTF features embellishments like ligatures and alternate characters-also known as glyphs-that exist to give designers more options to work with. For designers, both amateur and professional, the main useful difference between OTF and TTF is in the advanced typesetting features. They (OTF & TTF) are distinguished primarily by their different outline formats and the contrasting approaches employed to rasterize those outlines. There is no resemblance whatsoever to the old Postscript Type 1 font structures. The OpenType file format is basically the old TrueType file format that they added a couple tables to so they could stuff postscript outlines into it. IMO, that answers the OP's first question as well as can be expected so perhaps it is time to move on to the OP's second question, which as needs clarification before it can be answered? So, in this context (which may be Mac-only) I believe he is correct because in Mac-speak only "OpenType Postscript" fonts support these features & they all have the.
In Apple's Font Book app, all such fonts are identified as " OpenType PostScript," like below for Adobe Caslon Pro regular: I don't know what it is like for Windows but for the Mac OS, only. As he said, most fonts installed with the OS are Truetype fonts, which do not support OpenType features like Discretionary & Historic Ligatures, Historic Forms, Case Sensitive Forms, etc. I have no horse in this race but I believe trying to answer the OP's first question, which was about which fonts support "OpenType font features" in Affinity. In short: DWrights answer doesn‘t really help the initial poster, because his key question was, which fonts support open type features.