What is this I don't even know. Why does it exist? Why?
.d-flex
.d-inline-flex
.d-sm-flex
.d-sm-inline-flex
.d-md-flex
.d-md-inline-flex
.d-lg-flex
.d-lg-inline-flex
.d-xl-flex
.d-xl-inline-flex

Someone tried to bootstrap-ify flex I guess?

Feels a bit like pain

Weird flex but ok

Different flex behaviors based on screen size?

Vanilla CSS people trying to look cool

there is a lot you don't know that's why the internet is such amazing place where you can learn about everything.

I feel grumpy today, so let's be mean.
If you don't know about flexbox and bootstrap web development is maybe not for you.

Bootstrap - Flex
https://getbootstrap.com/docs/4.4/...

TailwindCSS set the trend for utility class-based CSS a few years ago

Use Tailwind

i assume it exists for the same reason that the whole flex system exists: to put patch on top of the css shitpile that attempts to kake it work in the way it should have been working from the start in the first place

Just use d-none and all your problem's solved.