I prefer 5. They both have forced weekly seasons but winter in 4 means snow everywhere which limits your car choices. In 5 you only get snow on top of one mountain instead of the whole map. Horizon 4 actually released in 2018 but didn't come to steam until 2021 so it's a fair bit older.
Do not hesitate irrespective of your tuning knowledge or racing skills! Tuning method: Stock look - stock wheel rims and size, no aero (unless absolutely necessary for handling and stability) Tuned for automatic/manual players by not skipping clutch+gearbox upgrades. Max performance with max handling possible.
Unpopular advice, but if Forza games are important to you I'd suggest dual booting. They run so much better on Windows. Both Horizon 4 and 5 are a locked 60 at native res, "high" present. And I do mean locked. Forza Motorsport 7 too. Horizon 3 runs like shit but then it always does.
When I got the game I bought the standard edition first to see if I would like the game before I spend all my money. Then later got the ultimate add-ons pack, which gives you the 2 DLC maps, vip pass, a few car packs and double exp that you would receive by buying the ultimate edition.
Sp0J.