Help with Cassuto commentary of Genesis 11:7 and 1:26

Hello, I’ve come across Cassuto’s commentary for Genesis 11:7 where he says that “let us go down” and “let us confuse their language” is the “plural of exhortation” and points us to his commentary on Genesis 1:26, where he goes in depth.

He says this about “let us make man”: “The best explanation, although rejected by the majority of contemporary commentators is that we have here the plural of exhortation (his exact wording is ריבוי של זירוזין ). When a person exhorts himself to do a given task, he uses the plural: ‘Let us go!’ ‘Let us rise up!’ ‘Let us sit!’ and the like. Thus we see in 2 Samuel 24:14: Let us fall into the hand of the Lord… but into the hand of man let me not fall; at the end of the verse, since a negation is expressed, the self-exhortation no longer obtains, and consequently the singular form appears again.”

I assume he’s talking about the Cohortative, but I’ve scoured everything I could find and I couldn’t find anything about using the plural for the singular.

The problem is, Cassuto just kind of says this with no sources. Like in that quote from Samuel, it just seems like the first verb is referring to the pestilence befalling David AND his land, while the second is referring to David alone fleeing from his adversaries.

So my question is: is this a real thing that’s actually documented anywhere?

I know it’s a huge topic right before Shabbat, but any information would be appreciated.