Preheat slow cooker on Low.

Heat 2 teaspoons oil in a skillet over medium-low heat and cook shallots until they are lightly browned, 5 to 10 minutes. Place in the slow cooker. Add beef to the same skillet and cook until meat is seared on all sides and browned, about 5 minutes. Add flour and mix well. Pour in beer and bring to a boil. Transfer beef-beer mixture to the slow cooker.

Wipe out the skillet with a paper towel and add remaining 2 teaspoons oil. Add onion and cook until soft and translucent, about 5 minutes. Add garlic and bacon and cook for 1 minute more. Transfer to the slow cooker. Add mushrooms and season generously with salt and pepper. Cover.

Cook on Low until meat is cooked through, about 5 hours.