There are a number of reasons why buybacks can increase prices. See https://www.mckinsey.com/business-functions/strategy-and-corporate-finance/our-insights/the

There are a number of reasons why buybacks can increase prices. See https://www.mckinsey.com/business-functions/strategy-and-corporate-finance/our-insights/the-value-of-share-buybacks#:~:text=Research%20from%20both%20academics%20and,of%20the%20shares%2C%20see%20prices https://www.mckinsey.com/business-functions/strategy-and-cor... for a list. All are second order effects.