How to specify the last existing column (in a range) in a formula?

Question

Google Sheets

Conventionally, there is such a situation:

In the first column of the formula, the values ​​​​are taken from the following.

New columns with new values ​​are added periodically.

You have to change the end of the range in the formula every time.

When values ​​are taken from rows, you can specify the letter of the column without an ordinal number, is it possible to do the same with a column?

Answer 1

entire line:
=SUM(1:1)
to end of line from column D:
=SUM(D1:1)
first 5 lines:
=SUM(1:5)

Answer 2

You can specify a column that you are unlikely to reach: AAA, for example.
=SUM(B1:AAA1)