Most of the people on Graphic Design Forum would be buyers of stock. If you want to know about the viability of being a stock seller, I suggest you ask at a photographers forum, such as https://www.microstockgroup.com/
I did it from 2005-2012 and it was a decent side income to my graphic design business. I uploaded my first batch and had 40 sales within a week. In 2005, there were about 10 million images available for licensing through the stock industry. Now it’s over a billion. Good luck getting noticed. If you don’t show up on the first few pages of a search return, you won’t get sales.
I quit in 2012 when they started pushing subscriptions. There wasn’t enough revenue coming in through stock sales to justify the time and expense of shooting. At one point I calculated my ROI. The work I put in during 2005-07 returned $400+ for every hour of labor I put in. Which was incredible. In 2012, it was bringing in around $3 an hour for stock work. It would have been a horrible financial decision to continue work at that rate of return, so I stopped.
I usually get about $0.33 for stock images that are acquired through subscriptions. I get 12% on the sale price. So, $24 on a $200 sale. The agencies give increased percentages of 20-35% if a contributor is exclusive to them.