It is more an RTS than a 'classical' wargame, but you could do it in Warzone 2100. It is old for now (but it was very fun in 2000s). It could be fun for you today. There is a free and open source version : https://wz2100.net/ . Source: 6 months ago

It's free at wz2100.net and it's tiny, mere megabytes. Source: 12 months ago

There is also Warzone 2100 as a freeware RTS if you want something else to play https://wz2100.net/. Source: 12 months ago

I never had any problems running it on mine, but Warzone is a very old game. Are you using the latest version? https://wz2100.net/. Source: about 1 year ago

Https://wz2100.net the best free and open-source rts ever. Optimised apple silicon processors. Source: about 1 year ago

But you can try https://isthereanydeal.com/ KEY Stores since they don't do regional pricing, everything priced USD (not MENA-USD) for all countries so Key will be giftable, if there's any for that D2 DLC. Source: 6 months ago

Isthereanydeal doesn't include key resellers at all. I prefer them. Source: 6 months ago

Even if you buy "new games" you can go to /r/patientgamers and https://isthereanydeal.com/ to get good prices and recommendations. Source: 6 months ago

If you cannot find it, fabricate it: you said that a steam activation code will work so get a cd case from a game or a dvd you already own, print a cover and swap it, buy rome 2 on a retailer site (they will all give you a steam activation code) and put the code inside the case; if you also want a prop cd then same story: find an empty cd, print the cd cover, cut it and glue it on the cd. Source: 6 months ago

Years of backlogs. If you want to know where to get free games check this out: https://isthereanydeal.com/. Source: 6 months ago