I think, especially if you're going for the 60s, ficticious is probably easier.
To any French person if you say "France in the 60s" their immediate reaction is going to be "may, 68" because that's the date of month-long protests that got so violent with police repression that the death toll is (i believe) unrivalled to this day. Of course the reasons for these protests didn't happen overnight, so you'd have to do quite a lot of research about where the general public was at in terms of appreciating the president and his policies. The 60s is also during the Algerian war, so a very specific to France type of racism was about (for example some of the children of early settlers born in Algeria came back to mainland France and despite being ethnically white were also discriminated against and treated like potential terrorists, along with native Algerians who came to France looking for work). There was a lot of political and social instability at the time, some of which like the algerian war is still contentious today, especially amongst older folks.
So, if you don't want to get into all that, i'd say work mainly on aesthetics. Both Arcane and Expédition 33 have done that pretty well in recent times, any French person will recognise Piltover's architecture as being from here, and COE33 wears its frenchness on its sleeve. Working on being period accurate with architecture, fashion, technology, transport, habits, etc... Will give a good sense of place and will be recognisable to locals while feeling grounded to foreigners. I personally don't have a problem with "this is an alternative universe 60s France" either, in my case I do just like a bit of flavour text to know why big events aren't happening/happen differently, so if you like worldbuilding and learning about history that can be a really cool middle ground.
I will also advise you try to watch some documentaries on the decade though. Not only to get a more in-depth exploration on what influenced art and culture back then, as well as getting good accuracy on what the decade actually looked like (it's really difficult to do accurate searches for this stuff now AI is mixed in and blurring everything together), but also depending on how serious/dark you want your story setting to be, there's plenty of political turmoil to give you springboards to inspire you.
General location guide if you want to stick with actual place names:
- Paris : incredibly vast cityscape, basically 7 cities in one, recognisable landmarks, main center for protests irl. Be aware the Louvre didn't have its pyramid yet
- Strasbourg : mix of strong French and German influence, like anywhere in Alsace, very pretty and recognisable buildings, big christmas market)
- Nice : biiiiig beaches, often sunny and hot, also quite influenced by its neighbouring Italy
- Golfe du Morbihan : not a city but a "zone" in Brittany with beautiful wildlife and natural scenery, includes a lot of "French Stonehenge" and druidic folklore and generally more countryside-y
- Marseille : pretty Paris-y, large city, but is closer to the coast. Also has a lot of gang activity if that's the vibe. It was also one of the centers for the Algerian War.
- Nantes : currently its reputation is a bit like that of Portland in the US, pretty permissive artist/student city. Big but not huge, especially back in the 60s. It can be an interesting place because a lot of our 19th century architecture was preserved from wwii bombing.
Also important to remember about France, especially if you're from the US:
- less cars, more bikes, loads of busses, especially in the 60s. Even in Paris a lot of people walk or take the metro.
- things are smaller, and trains were cheaper. Even if you set your character in one city, they can go pretty easily to another, even Paris/Nice takes 6-8h by train (crossing almost the entire country). The president also took holidays
- 100 year old buildings and older are pretty common, especially in places not bombed by nazis, so contemporary builds are sometimes slotted in between 18th and 19th century houses, that and renovations/extensions to old buildings can either be made to have a similar exterior to the old house or look like a modern one, so a lot of centuries can be mixed up in one building which can make it confusing to get good art reference from if you don't know what you're looking at
- art is everywhere, and it's often either renaissance-inspired or Art Nouveau inspired. If you're going on the more "fantasy" side of France, both of those will be good sources to worldbuild your own "kinda-france". Especially on the old houses and squares: sculptures, mosaics, things inspired by Edo Japan and Pompeii, protest graffiti, sculpted gates, metro entryways and doorknobs, for a long time something looking beautiful was a part of its functionnality. Lightposts is a fun one to look at too.
I hope this helps :3
