Thank you so much for the feedback! I will try and fix the issues with the drill and full screen when switching between mines. As well I will add an indicator as to what button should be used inside the forge (I swapped it to the space bar cause I feel it makes it easier for timing but I agree there should be an indication of that somewhere)
When it comes to the upgrades for auto miners and the crafted gemstones I wanted to add some upgrades that you could be bought with the crafted gemstones to have the associated mine continue to run in the background and gather materials but I was on a time crunch so I had to scrap it in order to get the initial release out within my 1 month time limit but now that its out I think while I start getting working on Month 2's game I may also add and fix some stuff here on Just a Game About Mining.
I also really like your idea of instead of having a unique icon for each smithy to have just one that you then can drag or select the gems you want to craft onto the anvil I think that would make it a lot more memorable and satisfying.
I plan to release a short devlog on this game and introduction to my challenge in the next few days so if you're interested the links will be put in the games description :)