Deuteronomy 7:26 refers to abominable objects. The chapter warns the Israelites never to make marriages between themselves and the surrounding pagans, then it specifies some of the abominable pagan objects they must destroy - altars, standing pillars, shrines and graven images. That is why the verse before the one you quote does not speak of people, but their idols, which are objects they worship - those objects must not be taken by the Israelites into their homes, but burned in fire by them. Neither are the Israelites to desire to keep the gold or silver smelted from them; they must not take the materials into their homes. Verse 26 does not speak of people.
Now, the question of Proverbs speaking of abominable qualities of people. It is not linked to that verse in Deuteronomy. Just because the word 'abominable' (or 'abomination') is in both passages does not mean they are both speaking about certain people who must not be brought into an Israelite house.
In Proverbs, there are actually 7 things that are an abomination to God. As you mention, a froward heart [the opposite of an upright heart] which is also a proud heart. Then there's the hallmark of 'tricky' business dealings (false balances), lying lips, wicked thoughts, wicked ways, twisted measurements, and justifying the wicked while condemning the just. Proverbs 11:1, 20; 12:22; 15:9, 26; 17:15; 20:10
Proverbs shows that a person with an upright heart will not DO those abominable things, which God can see, even if the wicked think they are getting off with their wickedness as other people cannot see as God sees. Proverbs is not dealing with the matters Deuteronomy chapter 7 is dealing with. You are trying to compare apples with oranges, spiritually speaking. Yes, both Bible chapters deal with spiritual 'fruit' (produce) but one is about pagan idolatry while the other is a warning to the people of God about the need for them to be upright in heart because God 'reads' the hearts of all, including theirs. God’s people should know that what people ARE is shown by what they DO, and that is how God’s people can learn to avoid those wicked people whose hearts are an abomination to God, even if they don’t worship idols.