"Be fruitful and multiply" is a blessing, not a command. It is a promise, not an order.
When the words are given in Genesis 1, they are given to all the living creatures that roam the earth and waters and sky.
To the animals:
וַיְבָ֧רֶךְ אֹתָ֛ם אֱלֹהִ֖ים לֵאמֹ֑ר פְּר֣וּ וּרְב֗וּ וּמִלְא֤וּ אֶת־הַמַּ֙יִם֙ בַּיַּמִּ֔ים וְהָע֖וֹף יִ֥רֶב בָּאָֽרֶץ׃
God blessed them, saying, “Be fertile and increase, fill the waters in the seas, and let the birds increase on the earth.” Genesis 1:28 (Revised JPS, 2023)
And to the humans:
וַיְבָ֣רֶךְ אֹתָם֮ אֱלֹהִים֒ וַיֹּ֨אמֶר לָהֶ֜ם אֱלֹהִ֗ים פְּר֥וּ וּרְב֛וּ וּמִלְא֥וּ אֶת־הָאָ֖רֶץ וְכִבְשֻׁ֑הָ וּרְד֞וּ בִּדְגַ֤ת הַיָּם֙ וּבְע֣וֹף הַשָּׁמַ֔יִם וּבְכׇל־חַיָּ֖ה הָֽרֹמֶ֥שֶׂת עַל־הָאָֽרֶץ׃
God blessed them and God said to them, “Be fertile and increase, fill the earth and master it; and rule the fish of the sea, the birds of the sky, and all the living things that creep on earth.” Genesis 1:28 (Revised JPS, 2023)
The words are repeated to Noah and his sons after they leave the ark, and the message is presented in Genesis 8 with regard to the animals first, and then in Genesis 9 to Noah and his sons.
But after God identifies himself as El Shaddai (God Almighty) to Abraham in Genesis 17:1, he clarifies the source of this fruitfulness: it is not of Abraham's work or strength, but of the strength of God that will bring about this blessing. Abraham will bear fruit because God will make it so.
וְהִפְרֵתִ֤י אֹֽתְךָ֙ בִּמְאֹ֣ד מְאֹ֔ד וּנְתַתִּ֖יךָ לְגוֹיִ֑ם וּמְלָכִ֖ים מִמְּךָ֥ יֵצֵֽאוּ׃
I will make you exceedingly fertile, and make nations of you; and kings shall come forth from you. Genesis 17:6 (Revised JPS, 2023)
In Genesis 35, God reveals himself in the same way to Jacob, and though the text does not say "I will make you" in this instance, the promise of El Shaddai has already been established: God will bring about the fruitfulness.
וַיֹּ֩אמֶר֩ ל֨וֹ אֱלֹהִ֜ים אֲנִ֨י אֵ֤ל שַׁדַּי֙ פְּרֵ֣ה וּרְבֵ֔ה גּ֛וֹי וּקְהַ֥ל גּוֹיִ֖ם יִהְיֶ֣ה מִמֶּ֑ךָּ וּמְלָכִ֖ים מֵחֲלָצֶ֥יךָ יֵצֵֽאוּ׃
And God said to him, “I am El Shaddai. Be fertile and increase; A nation, yea an assembly of nations shall descend from you. Kings shall issue from your loins. Genesis 35:11 (Revised JPS, 2023)