Reproduction steps:
1. Download and open the submitted project "AnimatorTimeScale.zip"
2. Open the Sample scene
3. Set the TimeScale to 1 (Edit -> Project Settings -> Time)
4. Enter Play mode and notice the speed at which the cube moves
5. Exit Play mode
6. Set the TimeScale to 0.1
7. Enter Play mode

Expected result: The Cube moves 10 times as slow as in step 4
Actual result: The Cube moves at the same speed as in step 4

Reproducible with: 2021.1.0a2, 2021.1.0b2, 2021.2.0a1
Not reproducible with: 2018.4.30f1, 2019.4.18f1, 2020.2.2f1, 2021.1.0a1

Notes:
Setting the Animator update mode to Animate Physics prevents the issue
Setting the TimeScale to 0 works as expected