C. F. Keil and Franz Delitzsch on Ecclesiastes 1:9

Ecc 1:9 “That which hath been is that which shall be, and that which is done is that which shall be done; and there is nothing new under the sun.” - The older form of the language uses only אשׁר instead of מה־שּׁ, in the sense of id quod, and in the sense of quid-quid, אשׁר כל (Ecc 6:10; Ecc 7:24); but mǎh is also used by it with the extinct force of an interrogative, in the sense of quodcunque, Job 13:13, aliquid (quidquam), Gen 39:8; Pro 9:13; and mi or mi asher, in the sense of quisquis, Exo 24:14; Exo 32:33. In שׁ הוא (cf. Gen 42:14) are combined the meanings id (est)quod and idem (est)quod; hu is often the expression of the equality of two things, Job 3:19, or of self-sameness, Psa 102:28. The double clause, quod fuit ... quod factum est, comprehends that which is done in the world of nature and of men-the natural and the historical. The bold clause, neque est quidquam novi sub sole, challenges contradiction; the author feels this, as the next verse shows.