On Mac, collections.abc is imported at startup time via site.py (which imports rlcompleter, which imports inspect, which imports collections.abc). I'd guess it's the same on Linux.

mdickinson@mirzakhani cpython % ./python.exe
Python 3.11.0a2+ (heads/main:76d14fac72, Nov 10 2021, 15:43:54) [Clang 13.0.0 (clang-1300.0.29.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys; "collections.abc" in sys.modules
True
>>> ^D
mdickinson@mirzakhani cpython % ./python.exe -S
Python 3.11.0a2+ (heads/main:76d14fac72, Nov 10 2021, 15:43:54) [Clang 13.0.0 (clang-1300.0.29.3)] on darwin
>>> import sys; "collections.abc" in sys.modules
False
>>> ^D