I'm not 100% sure what you mean by "low spec" because that's down to opinion and could mean almost anything. That aside, there's plenty of f2p games where their graphics can be altered massively to adhere to the spec of your computer.
There are games Such as War Thunder and Warframe, which are available on PS4 and PC.
There's also games such as Neverwinter, Team Fortress 2, League of Legends etc. Look on steam, they have their own f2p section. Easiest way to see if they run is to try them.