Giant lists of house rules in 5E is another good "red flag" for me from a DM, especially if they try to minimize them, or can't explain them rationally. I have met people who have a bunch of house rules and run a good game, but it's usually a highly stylized one with a very specific focus, and they know it, and can explain all their choices. I've come across more people who have a ton of house rules and most of them make no sense, often contradicting each other (sometimes literally, sometimes thematically), or worst but perhaps most common, they have a bunch of house rules to "cover stuff the rules don't", when the rules actually do cover that, often with a near-identical rule, but they clearly don't know that.