To replace the current big tech business, I have a few suggestions:
Use FOSS (Free and open source software)
If this is not possible, try to find software that does not invade your privacy and made by a smaller company
Try to avoid paying privacy invading companies. I’m not saying never pay for proprietary software, but try to only spend the money on ones that respect you.
Spread the word about good FOSS apps
Donate to FOSS
Vote for politicians who are serious about antitrust
If you have the skills, contribute to FOSS or make your own software!
Use adblockers on websites that don’t respect you and/or your privacy