Reproduction steps:
1. In the hierarchy window, right mouse click > Light > Directional Light
2. In the menubar, Window > Sequencing > Timeline, then click Create in the Timeline window and save the new asset
3. Enter recording mode on the Directional Light Animator in the Timeline
4. Change the 'Indirect Multiplier' value in the Light component inspector

Expected: a new key should be added
Actual: nothing happens

Same bug with the 'Cookie' property on the light also.
Can be reproduced on Unity 2020.2.0b1 with Timeline 1.2.15