I would say that the Reddit OP made a few choices that led to his situation:

• Going to school for a BFA — not exactly a guarantee of a high-paying career.
• Taking out large student loans that resulted in $1100/month payment (assuming a 6% interest and a 10-year term, this implies nearly $100k in debt!!!) — it’d be different if this was to get a degree that leads to multi-6-figure incomes (e.g., surgeon, investment banker, etc.), but for a bachelor in fine arts, this is an extreme level of indebtedness.
• Taking on way too much debt (related to the previous point) — between the mortgage, auto loan, and student debt, he’s paying almost 77%(!) of his after-tax income. It’s not clear how he could possibly have qualified for his mortgage, given that lenders require a much lower ratio between total debt service and income (less than 45% if memory serves).

I mention all these not to bash the OP, but rather to help others see the connection between choices and their consequences, which may help them make more informed choices.

Regarding your three suggested changes, I agree that he has to reduce his costs, and those options could help (though becoming an Uber driver and selling his car are not compatible with each other :)).

Considering that he already feels like he’s working “day and night,” taking on a side hustle seems to be beyond him, at least at the moment. If he does take something on, it should be something that pays more per hour than his job (i.e., more than $30/hour) after expenses, which rules out Uber, Lyft, or driving last-mile deliveries for Amazon.

Taking a roommate seems to be most doable, and could save him at least half of his ~$1600/month in housing and utility costs. That would drop his cash outflow from its current level of $200/month greater than his income to $600 less than his income.

It’s not clear that selling the car would be a long-term benefit. If he’s close to paying off the auto loan, he might soon be in a situation where his transportation costs would potentially increase rather than decrease by selling the car. Using public transport might also increase his commute time.

One thing he could do immediately is look for a “pro-bono therapy project” therapist, if there is such in his area. This could reduce his expenses by $250/month.