Here is every career start against the Cubs:
2020:
3 IP, 4 ER, 3 H, 2 BB, 3 K
2021:
5 IP, 0 ER, 1 H, 4 BB, 8 K
6 IP, 1 ER, 2 H, 2 BB, 10 K
4 IP, 2 ER, 5 H, 1 BB, 7 K
6 IP, 2 ER, 2 H, 4 BB, 8 K
5.1 IP, 2 ER, 5 H, 2 BB, 8 K
2022:
4 IP, 3 ER, 3 H, 4 BB, 6 K
6 IP, 2 ER, 4 H, 3 BB, 5 K
6 IP, 0 ER, 0 H, 1 BB, 5 K
2023:
5.1 IP, 3 ER, 4 H, 3 BB, 10 K
2024:
5 IP, 3 ER, 3 H, 6 BB, 5 K
5.2 IP, 1 ER, 3 H, 2 BB, 11 K
7 IP, 1 ER, 2 H, 2 BB, 8 K
2025:
6 IP, 0 ER, 4 H, 1 BB, 7 K
Overall: 14 starts, 2.91 ERA, 4.9 H/9, 1.05 WHIP, 12.2 K/9
-10 of 14 starts allowing 2 ER or less
-13 of 14 starts allowing 3 ER or less
The one he allowed more than 3 ER was early in his career and an emergency start as he was mostly a reliever that year.
Cubs are actually "only" 5-9 when Peralta starts which seems decent considering his overall numbers against him.