Use their software less. The attention economy is important for tech companies. If their metrics decrease, they might respond to that signal. Additionally, if someone watches you use an alternative software then they might also be inspired to switch. Using bad software less sends a negative signal to the company and a positive signal for the alternatives that you support.
After repeated security compromise of iOS devices, tested GrapheneOS on Pixels. Better security, but user experience painful to the point of unusable, i.e. tasks could not be completed. Conclusion: GrapheneOS on Pixel phone+tablet (for secure workflows) and iOS/iPadOS for everything else.
Even with substitutes, I think there are barriers. Bundling and the way these companies do pricing means substitutes are ineffective. Switching costs of different kinds exist. Network effects prevent substitutes from being truly competitive. And so on.
