Here we cover the better performances by those who made their debut in the calendar year 2021.
Batting:
40 or more runs in an innings:

Note the double centuries by KR Mayers and DP Conway. Only 7 players have made a double century on debut.
Mayers and Bonner combined to enable the West Indies to chase down 395 in the last innings:
SS Iyer and Abdullah Shafique scored 50+ in both innings.
80 or more runs in a match:

Bowling:
4 or more wickets in an innings:

Headed by SM Boland’s 6-7 at the end of the year. There are others who have made 7wi and 8wi on debut, but this would probably be the most influential bowling performance by a debutant-as it reduced England to 68 all out and secured the Ashes for Australia.
7 or more wickets in a match:

P Jayawickrama took 11 wickets on debut, while Boland had the best figures of those who took 7 wickets.
Fielding:
2 or more dismissals in an innings:

Note AT Carey’s 5 and 3 in the same match.
3 or more dismissals in a match.

AT Carey took 8 dismissals, equalling the record by HB Taber and CMW Read.
However, Carey is the only one to take 8 catches on debut, as the others had 7 catches and a stumping.
Several fielders (including Boland again!) took 3 catches in a match.
All-round performance:
50 runs and 4 wickets in match:

Only one instance, and he has not played for the past few months.
50 and 3 dismissals in match:

Note that Abdullah Shafique made two fifties in the match, besides taking 3 catches.