The issue you're experiencing with the "K" key not automatically placing a keyframe might be related to how the "Key Edited" function works. The "K" key is used to set keys for properties that have been edited. If you haven't made any changes to the properties of the bones or slots, pressing "K" won't set a keyframe. Ensure that you have made some changes to the properties you want to key before pressing "K". Additionally, check if the "Auto Key" feature is enabled, as it can automatically set keys when changes are made, which might interfere with manual key setting.

NapperC Note that Frame Keys, one of the hotkeys that has no keys assigned by default, is a hotkey for adjusting the zoom in the Dopesheet view, not for recording keys. The key K is then assigned by default to a hotkey called Key Edited. This is a hotkey that, as Spinebot explained, can be pressed after changing any value to add a key for the edited property. The hotkeys for adding keys are under the "--- Keying ---" section:

Use L (Key Active) if you want to add a key for the currently active tool.