Bible Gateway:
https://www.biblegateway.com/passage/?search=Proverbs+19&version=AMP
Bible Hub Commentary Proverbs 19:19-21
https://biblehub.com/commentaries/proverbs/19-21.htm
Ellicott's Commentary for English Readers:
(21) There are many devices (or, thoughts) in a man’s heart.—“He disquieteth himself in vain” (Psalm 39:6), endeavouring to carry out his various plans in life, while the one unchangeable “counsel of the Lord,” that shall stand—i.e., abide in all its fulness. (Comp, Isaiah 46:10-11; Psalm 33:11; Job 23:13.)
Benson Commentary:
Proverbs 19:21. There are many devices in a man’s heart — Which shall not stand, but be disappointed; many designs and contrivances, which he thinks to be so well devised and planned that they cannot miscarry. Nevertheless, the counsel of the Lord — Which oft-times contradicts, and therefore overrules or defeats the designs and purposes of men; that shall stand — Shall certainly be fulfilled, and bring to pass whatever he pleases.
Matthew Henry's Concise Commentary:
19:19. The spared and spoiled child is likely to become a man of great wrath. 20. Those that would be wise in their latter end, must be taught and ruled when young. 21. What should we desire, but that all our purposes may agree with God's holy will?

Barnes' Notes on the Bible:
Contrast the many purposes of man, shifting, changing, from good to better, from bad to worse, and the one unchanging righteous "counsel" of Yahweh.