If Jehovah is the 'son of man', who is the 'Ancient of Days/that One'?
The God Almighty, Most High. There was a genuine difference between camps of scribes. Some saw Yahweh as an emanation/agent/son of El Most High while some like 2nd Isaiah and a couple Psalm writers combined the two. These two ideas appear to have been in tension in the 5th century forward. It seems an idea only recently becoming popularized. Most research assumes the Most High's delegation of Israel to Yahweh in Deut 32 reflects a very early form that somehow escaped the editors. It might rather actually reflect a later theological development (or possibly preserved with that new interpretation), where the Most High is far too transcendent to interact directly with material things and He uses the agency of a Logos/Son.
It is important to realize that not every writer shared this concept in identical ways. IOW, the writer describing Logos may not have had in mind all the other names/terms used by other writers in different contexts. Each pericope was meant to be understood in its own context. I'm not therefore sure we should assume the writer of Dan 7 understood Yahweh as identical with the SofM/Michael.
It gets messy. Daniel is a composite work made up of centuries old stories combined with apocalyptic elements from the Maccabean period. It also went through some editing in the years following. Notice in chapt 9, the only section that mentions 'Yahweh', and how even in this section the use is inconsistent. It's difficult to understand the motives but it would seem some editing is involved. IOW, did the writer of the apocalyptic sections (or even just chapt 9) use the tetragrammaton (my/our God YHWH) of not? If so, did he differentiate him from the 'Most High' the expression in Chapts 3,4,5 or the 'God of heaven', 'Lord of Kings' and 'God of Gods' in chapt 2 or 'Ancient of Days' in 7?