(יא) וַהֲקִמֹתִ֤י אֶת־בְּרִיתִי֙ אִתְּכֶ֔ם וְלֹֽא־יִכָּרֵ֧ת כׇּל־בָּשָׂ֛ר ע֖וֹד מִמֵּ֣י הַמַּבּ֑וּל וְלֹֽא־יִהְיֶ֥ה ע֛וֹד מַבּ֖וּל לְשַׁחֵ֥ת הָאָֽרֶץ׃ (יב) וַיֹּ֣אמֶר אֱלֹקִ֗ים זֹ֤את אֽוֹת־הַבְּרִית֙ אֲשֶׁר־אֲנִ֣י נֹתֵ֗ן בֵּינִי֙ וּבֵ֣ינֵיכֶ֔ם וּבֵ֛ין כׇּל־נֶ֥פֶשׁ חַיָּ֖ה אֲשֶׁ֣ר אִתְּכֶ֑ם לְדֹרֹ֖ת עוֹלָֽם׃ (יג) אֶת־קַשְׁתִּ֕י נָתַ֖תִּי בֶּֽעָנָ֑ן וְהָֽיְתָה֙ לְא֣וֹת בְּרִ֔ית בֵּינִ֖י וּבֵ֥ין הָאָֽרֶץ׃ (יד) וְהָיָ֕ה בְּעַֽנְנִ֥י עָנָ֖ן עַל־הָאָ֑רֶץ וְנִרְאֲתָ֥ה הַקֶּ֖שֶׁת בֶּעָנָֽן׃ (טו) וְזָכַרְתִּ֣י אֶת־בְּרִיתִ֗י אֲשֶׁ֤ר בֵּינִי֙ וּבֵ֣ינֵיכֶ֔ם וּבֵ֛ין כׇּל־נֶ֥פֶשׁ חַיָּ֖ה בְּכׇל־בָּשָׂ֑ר וְלֹֽא־יִֽהְיֶ֨ה ע֤וֹד הַמַּ֙יִם֙ לְמַבּ֔וּל לְשַׁחֵ֖ת כׇּל־בָּשָֽׂר׃ (טז) וְהָיְתָ֥ה הַקֶּ֖שֶׁת בֶּֽעָנָ֑ן וּרְאִיתִ֗יהָ לִזְכֹּר֙ בְּרִ֣ית עוֹלָ֔ם בֵּ֣ין אֱלֹקִ֔ים וּבֵין֙ כׇּל־נֶ֣פֶשׁ חַיָּ֔ה בְּכׇל־בָּשָׂ֖ר אֲשֶׁ֥ר עַל־הָאָֽרֶץ׃ (יז) וַיֹּ֥אמֶר אֱלֹקִ֖ים אֶל־נֹ֑חַ זֹ֤את אֽוֹת־הַבְּרִית֙ אֲשֶׁ֣ר הֲקִמֹ֔תִי בֵּינִ֕י וּבֵ֥ין כׇּל־בָּשָׂ֖ר אֲשֶׁ֥ר עַל־הָאָֽרֶץ׃ {פ}

(11) I will maintain My covenant with you: never again shall all flesh be cut off by the waters of a flood, and never again shall there be a flood to destroy the earth.” (12) God further said, “This is the sign that I set for the covenant between Me and you, and every living creature with you, for all ages to come. (13) I have set My bow in the clouds, and it shall serve as a sign of the covenant between Me and the earth. (14) When I bring clouds over the earth, and the bow appears in the clouds, (15) I will remember My covenant between Me and you and every living creature among all flesh, so that the waters shall never again become a flood to destroy all flesh. (16) When the bow is in the clouds, I will see it and remember the everlasting covenant between God and all living creatures, all flesh that is on earth. (17) That,” God said to Noah, “shall be the sign of the covenant that I have established between Me and all flesh that is on earth.”

Rashi learns from the word לְדֹרֹת (for generations) that it is just for "faulty" generations because in לְדֹרֹת is missing the letter "vav"/ "ו" (correct דּוֹרוֹת).

Only the "faulty" generations need a sign and the generations of Zadikim don't need signs. For example the generations of Hezekiah, king of Judah, and the generation of R. Shimeon ben Yochai.

From this we can learn that only because we are not full Zadikim we see the signs like the rainbow and through Tshuva and the Mizvot we can slowly rise our level that we don't need the Rainbow and other signs,