I would also have a chat with your partner and agree on what types of things you both don't find appropriate.
E.g. is violence/fighting in games appropriate? Sexual themes? Battles? Gothic/fantasy content? Blood/gore? Online play with strangers? In game gambling mechanics? Swearing? Guns? Etc.
Ratings are good but they aren't specific to what you personally deem appropriate.
E.g. I would never give my little boy fortnite. It's rated 12, but full of addictive, violent, online interactivity etc.
Yet I would absolutely let him play a total war game, even though many have ratings of 16.. they are big strategy games where you control armies and grow a nation, etc. yes technically they have battles and they touch upon worldly issues when you are managing your nation, but they aren't designed to be addictive, don't need to be online, encourage critical thinking and strategy, and learning about history (many are set in historical settings, rome, Napoleon etc.
My point is, by the letter of the ratings the grand strategy games are worse.. but personally I feel far more comfortable with them than the more "suitable" games that hide a lot of risky and adult things behind cartoonised visuals.
In your examples, personally I wouldn't be bothered by the fantasy parts of what you mention. A necromancer that brings people back from the dead is fairly common fantasy, they have been in books, comics and board games that my son has played... But I don't like the level of blood/gore in those games, and the demonic themes go a bit too far for me. (Although id still prefer my son plays that co-op with his father than sits getting addicted to Roblox or something similar)