My only expenses are gas and time. Obviously there are occasional car repairs and oil changes. I've cut that down mostly by learning to fix my own car and doing my own oil changes (thanks YouTube!). Generally, I'd say my expenses are about 7% of my income. If you did this long term you would probably need to get a new car every 5 years or so, but you can get a pretty decent used car for around $5k, so factor that in as well.
Last year I made around $35k on the delivery apps, I was able to write off about $10k, and then I owed $3k in taxes. So in total I made around $30k, but I also did not work much over the summer.
The best way to stay busy, stack orders, & make money is to work the rushes: lunch & dinner. I can usually make around $50 for lunch and $150 for dinner, sometimes more. That's 11a-1p and 5:30p-10p. I just work dinner though because I'm a night owl and like to stay up late. The time required varies. For me, it takes around 35-40 hours to make $1000. I'm an expert though, so it might take longer for other people.
Although I should mention that I don't work that much anymore. The delivery apps are best used as a side hustle or as a means to an end ie between jobs or in my case, to provide the freedom toward starting your own business. Nowadays, I mostly just work on the weekends.
Lastly, I DON'T think things will level off after Covid. If anything it's made people more aware of the delivery apps. Since I started 2 1/2 years ago, I've noticed an upward trend in usage and I think that will only continue to go up. Paying an extra $5-$7 bucks to have food delivered seems to be worth it for a lot of people.