How to pass the name of the sheet from the cell to the formula in Google spreadsheets?

Question

Google

In the example in the screenshot, column A shows the names of the sheets, how can you substitute the name of the sheet from the cell, for example A8, into the formula, because options: =COUNTIFS(A8!D8:D;INDEX($1:$1;1;COLUMN()))
=COUNTIFS(A8&!D8:D;INDEX($1:$1;1;COLUMN()))
=COUNTIFS(A8& '!D8:D';INDEX($1:$1;1;COLUMN()))
=COUNTIFS(A8&"!D8:D";INDEX($1:$1;1;COLUMN()))
- don't work

Answer 1

Use the INDIRECT function

=COUNTIFS(INDIRECT(A8 & "!$D:$D");INDEX($1:$1;1;COLUMN()))