Google-sheets – Show number in a cell – based on a value from another cell

Google Sheets could be expanded to implement "a formula approach" for certain tasks. This is called "custom functions".

Custom functions should only be used to display values, so they should not be used to set the conditional formating directly. Instead use the conditional formatting built-in feature.

References

• Custom Functions in Google Sheets - Apps Script Guides
• Apply conditional formatting rules - Docs editors Help

With the magic of matrix multiplication and this solution (credit where credit is due), I have managed to wrangle it to do what you want.

=ArrayFormula(IF( J4:J = "" ; "" ; MMULT((ROW(G4:G)>=TRANSPOSE(ROW(G3:G)))*((ROW(G4:G)+1-I4:I)<=TRANSPOSE(ROW(G3:G)));G3:G)* ( ( J4:J ) / 10 ) ))

My head hurts already, so I won't go into too much explanatory detail, except to say that the key magic happens in

="MMULT((ROW(Range1)>=TRANSPOSE(ROW(Range2)))*((ROW(Range1)+1-I4:I)<=TRANSPOSE(ROW(Range2)));Range2)))"

And I've added a second sheet to your public one with a rough equation builder, for understanding or alternative applications.