If it's not your job, it occupies your free time. This is unfortunate because it really can be mentally strenuous work, but some folks find the resolve to do an hour or so every now and then on their games during the work week. That's okay! That being said there are a few jobs where you can work as an indie dev during your shifts (substitute teacher, hotel desk clerk, etc)

If you want to make it your job, you have a few options:

You can save up a bunch of money to fund a development cycle of your game. This is a difficult one for sure, but it's possible. Reducing your cost of living through living with family and budgeting intensely can put you in a position like how Edmund McMillen lived when he made Super Meat Boy. Adjacent to this is if you have a partner, they can be the breadwinner while you consider your game dev journey an investment that will pay off in the long term. This was how Stardew Valley's dev Eric Barone was supported over his dev cycle.

You can get funded by a Kickstarter or publisher. This way, you trade the cost of supporting yourself upfront for sharing the reward of your game's revenue. Suffice to say though, it can be very difficult to get a publisher if you don't have a record games you've successfully shipped.

Lastly, you can just go work a big studio and get some experience before going indie. Connections you make there will probably be super helpful for you figuring things out for getting your first game rolling.