Tally form

You can use the embed url that tally generates and paste it in Notion as an embed block.
The result will look like this:

Dark mode

The embedded form will also support dark mode, inverting the colors of the embedded form when the color mode is dark.

Remove the scroll bar

To make sure there is no scroll bar make the block height as tall as you can, this way the iframe block will always have space and no scroll bar will show up.