Unlike many other occasions where Hashem reacted retroactively either favorably or not, in this Parasha there's no mentioning of Hashem's reaction.
What was Hashem's reaction to Yitroh's advice and Moses' actions?
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Shout out to DanF for being Mechavein to many of the Mefarshim:
Rashi, Ibn Ezra, and others assume that the words Vetizvecha Elokim (Shemos 18:23) that Yisro said mean "and if God will command you to do this", in which case, Moshe's doing it implies that Hashem approved.
Rav Avraham Ben Harambam (to 18:24, use above link) notes that there seems to be a repetition about Moshe carrying out this arrangement, which he says is a reference to Hashem agreeing.
See my answer to your other question to see which Mefarshim disagree with the above and explain why Moshe would not have asked Hashem, although this seems to be the generally accepted opinion.
Rav Hirsch explains that unlike Rashi and Rashbam as cited by @רבות מחשבות this is the way in which it would properly allow Moshe Rabbeinu to receive the commands from Hashem and allow the people to receive them and understand them.
Rav Hirsch translates Yisro 18:23
אִ֣ם אֶת־הַדָּבָ֤ר הַזֶּה֙ תַּעֲשֶׂ֔ה וְצִוְּךָ֣ אֱלֹהִ֔ים וְיָֽכׇלְתָּ֖ עֲמֹ֑ד וְגַם֙ כׇּל־הָעָ֣ם הַזֶּ֔ה עַל־מְקֹמ֖וֹ יָבֹ֥א בְשָׁלֽוֹם׃
If thou doest this, then Hashem can give thee His Commands and thou shalt be able to endure; and all this people too, each one in peace shall come to his befitting position.
Rav Hirsch, says that this will then allow everyone to
arrive at the place and position to which they are really meant to come.
The reason for this is
That this really expresses the whole true work of a judge, viz. to direct everybody and everything to the standpoint and place it should occupy, to bring them there, and establish it or them securely on it.
Thus, instead of needing an explicit commandment, this is the best way to implement the commands already received and to set up the system of justice that Hashem had commanded already.