Honeygain is free software that shares your unused internet connection for profit.  According to the site's calculator, you can earn about $3 per month for each GB of data shared per day.  All you have to do is download the software (referral link), install it and set up your account.  If you want to earn even more, you can enable content delivery, but I'm still queued for this service so I'm not 100% sure what it does.  I suspect an ad delivery system similar to Brave browser's "Brave Rewards" program.

   The site claims to have no access to users' device storages, so you can earn without worrying about the security of your personal files.  Malwarebytes didn't flag it, so I'm reasonably certain this is true.  Connections through Honeygain are encrypted as well.  I've been using it for almost a month and have had no security issues (that I know of).

   If you have unlimited data through your ISP or mobile carrier, Honeygain could, if nothing else, work to offset the cost of service.  I live in a very remote part of the US, so I don't get much traffic, but users in areas of high demand should easily outperform me in earnings (I've accrued about $3 of credit so far and need $20 to withdraw).

   You're not likely to get rich off of this program, but I can see no reason why you shouldn't get paid for the data you don't use, especially since this program is free to use.