Yeah, we’re all hoping that this is just a major bug. There’s no way that they could have overlooked such an important detail. Be sure to report this ASAP to support@airtable.com.
I have a used Long Text fields with Markdown added to my interface as Editable fields, and as I write the entire text box grows to accommodate all entered text. Below is what I see just copying/pasting random text in;

Long text boxes will expand as needed and stay expanded.

And here’s the same field after I paste a long piece of text into it (and then exit the field).

Not sure what’s going on with the images I pasted. The second image has been scaled down. But you can see (I hope) that the original field was very small (when it only contained “This is the default size of the field”) but expanded a great deal with I pasted several paragraphs of text and then exited.
This seems like the right way to behave to me.
Long text boxes will expand as needed and stay expanded.

And here’s the same field after I paste a long piece of text into it (and then exit the field).

Not sure what’s going on with the images I pasted. The second image has been scaled down. But you can see (I hope) that the original field was very small (when it only contained “This is the default size of the field”) but expanded a great deal with I pasted several paragraphs of text and then exited.
This seems like the right way to behave to me.
Oh, this is great news! Hooray!!
Long text boxes will expand as needed and stay expanded.

And here’s the same field after I paste a long piece of text into it (and then exit the field).

Not sure what’s going on with the images I pasted. The second image has been scaled down. But you can see (I hope) that the original field was very small (when it only contained “This is the default size of the field”) but expanded a great deal with I pasted several paragraphs of text and then exited.
This seems like the right way to behave to me.
@WilliamPorterTech thanks, that solves it. There’s no control over precise field length, but all entered text will be visible. Thanks.