Physicist Sabine Hossfelder posted on YouTube an interview titled:
How good is the evidence for Dark Energy?
Redshifts are mentioned several times, including the M31 anomaly.
The Doppler effect is observed with the light source in motion.
A galaxy has millions of stars with independent motion so a galaxy redshift requires a different interpretation.
This mistake with galaxy redshifts was noted by Hubble in the 1930's but never fixed.
The correct Doppler effect usage is explained here: