Sorry to add on to an already too-long comment, but if I may humbly suggest:
- The most recently acquired inventory item should be "active" automatically.
- The primary mouse button should either view, pick up or activate whatever interactable element is under the reticle. Right mouse button could maybe cycle through inventory items, or deactivate an item if that function is needed (although it shouldn't be).
- If an item is active, primary mouse button should also serve to use that item (like a key) on whatever interactable element is under the reticle (lock).
- On combination lock puzzles, you might want to give some basic player instructions, like "type in the answer and hit enter," because currently it is not very clear how you want players to input codes. (Also, I can only seem to input digits from the number row, and not the numpad. Can't imagine why that is.)