How to Autofill last row with formula, when data is received from IFTTT on the last row?

This is a very common problem when dealing with auto-inserted data through sheets api or Google forms. The easiest solution would be to convert all your formulas into arrayformulas. For eg, Your formula in D2

=MID(C2,1,2)&"."&MID(C2,3,2)&".2020

can be modified as

In D1:

=ARRAYFORMULA({"Extracted Date";MID(C2:INDEX(C:C,COUNTA(C:C)),1,2)&"."&MID(C2:INDEX(C:C,COUNTA(C:C)),3,2)&".2020"})

OR using regex:

=ARRAYFORMULA({"Extracted Date";REGEXREPLACE(C2:INDEX(C:C,COUNTA(C:C)),"(\d{2})(\d{2}).*","$1.$2.2020")})

The table then becomes:

|    | C                               | D                                                                                                                   |
|----+---------------------------------+---------------------------------------------------------------------------------------------------------------------|
| 1> | From IFTTT                      | =ARRAYFORMULA({"Extracted Date";MID(C2:INDEX(C:C,COUNTA(C:C)),1,2)&"."&MID(C2:INDEX(C:C,COUNTA(C:C)),3,2)&".2020"}) |
| 2> | 0809 1800 0909 0600 RLK Steiger |                                                                                                                     |
| 3> | 0809 1800 0909 0600 RLK Dvorak  |                                                                                                                     |
| 4> | 0909 0600 0909 1800 UNIS Brando |                                                                                                                     |

Here the rest of D:D is auto filled automatically.

• We use array literals on the header row: {"Extracted Date";Formula for rest of the column}

• Whenever a new row comes, INDEX/COUNTA() auto calculates the last row and automatically fills the formula upto last row. See here for a deeper explanation on INDEX/COUNTA.