The Hebrew word translated "bless" is simply בָרַךְ (barak) and in almost all cases is just a series of well-wishes for a person. Indeed, the LXX translates this word as εὐλογέω (eulogeo) which is literally, "good words", or, "good thoughts".
The word occurs frequently in the OT, eg, Gen 1:22, 28, 2:3, 5:2, 9:1, 26, 12:2, 14:19, 17:16, etc.
There are some important exception to this - when the blessing was pronounced by either a prophet under inspiration or by God Himself, then the bless often (but not always) contained a prediction about future prosperity or otherwise. This occurred when Isaac blessed Jacob (Gen 27, 28) and when God bless Adam and Eve (Gen 1:28), etc.
However, in the case of Jacob blessing Pharaoh (Gen 47:7, 10), the content of what was said is not recorded. Therefore, all that can be assumed is that Jacob essentially wished Pharaoh well and general good prosperity, etc.
The interesting thing here is the comment in Heb 7:7 about the "greater blessing the lesser". It is obvious that Jacob, because he realized that he served a sovereign of the universe who was infinitely great that the monarch of Egypt, was consciously superior and so was able to bless Pharaoh.
The pulpit commentary says this -
And Jacob - in reply probably to a request from Pharaoh (Tayler
Lewis), but more likely sua sponte - blessed Pharaoh. Not simply
extended to him the customary salutation accorded to kings
(Rosenmüller, Kalisch, Alford, and others), like the "May the king
live for ever!" of later times (2 Samuel 16:16; 1 Kings 1:25; Daniel
2:4; Daniel 3:9, &c.), but, conscious of his dignity as a prophet of
Jehovah, pronounced on him a heavenly benediction (Murphy, 'Speaker's
Commentary,' and others) - hoe verbo non vulgaris et profana salutatio
notatur, sed pia sanctaque servi Dei precatio (Calvin). Genesis 47:7