• Operating system and version (Windows, macOS, Android, iOS) - N/A
• Browser and version (Chrome, Firefox, Safari, Microsoft Edge, Opera, Android Browser) - N/A

I noticed there is a breaking change, related to the media-breakpoint-down() mixin, which is not included in the Migration Documentation

In Bootstrap v4 the media-breakpoint-down() was triggered at the next larger breakpoint, but in Bootstrap v5 this is changed.

Example:
Bootstrap v4 - when using media-breakpoint-down(md) - the breakpoint is equal to @media (max-width: 991.98px) Bootstrap v5 - when using media-breakpoint-down(md) - the breakpoint is equal to @media (max-width: 767.98px)

Codepen Example:
Bootstrap v4 - https://codepen.io/petia182/pen/qBrMBKo
Bootstrap v5 - https://codepen.io/petia182/pen/wvJEvLa