These are the players who made their Test debut in 2020:

This list is in chronological order of debut.
No really outstanding performances. We look through the good performances:
Batting: 40 or more in an innings:
PJ Malan (SA) 84 v E
KT Kasuza (Z) 63 v SL
Hasuranga de Silva (SL) 59 v SA
J da Silva (WI) 57 v NZ
GD Philips (NZ) 52 v A
S Gill (I) 45 v A
KA Jamieson (NZ) 44 v I
80 or more in the match:
PJ Malan (SA) 89 v E
S Gill (I) 80 v A
While Malan has the best innings and match scores, he is not in the current Test team of SA. Similarly Philips is not in the current NZ team. Gill is likely to make further progress, as he did with 91 in the decisive Test at Brisbane.
Bowling: 4 or more wickets in an innings:

The only fiver is by BE Hendricks, who is not in the current SA team. Jamieson with 4-39 can be said to be the bowling find for NZ, as he went on to make a 10-for.
8 or more wickets in the match:
None. The best are
6-100 by L Sipamla (SA) v SL
6-175 by BE Hendricks (SA) v E
5-77 by Mohammed Siraj (I) v A
Fielding: Most dismissals in an innings:
2 by J da Silva (WI) and by Mohammed Siraj (I)
Most dismissals in a match:
Again, 2 by J da Silva (WI) and by Mohammed Siraj (I).
da Silva is a keeper and Siraj is not.
Oddly, no one made a stumping on debut this year.
Best all-round performances:
KA Jamieson (44, 4-39) and 1 catch
Hasuranga de Silva (59, 4-171) and 1 catch.
Clearly Jamieson had the more impressive all-round debut.