Over time, saving keymaps fragments the memory. In the "Tools" tab of VIA, run "Clear EEPROM" and re-upload your saved JSON file. This fixes random key misbehaviors.
Most users only use Layer 0 (base) and Layer 1 (Fn). Program Layer 15 as a "transient" layer that activates only while holding a specific key. This lets you create a completely different keyboard layout for Photoshop or Excel without toggling. magic+refiner+mk21+keyboard+software+top
The top productivity feature is the "App-Detect" profile. Over time, saving keymaps fragments the memory
Note: You must flash your MK21 with a VIAL-compatible firmware. This is a one-time process, but it voids certain warranties. Only proceed if you are a confirmed enthusiast. magic+refiner+mk21+keyboard+software+top