Personally, this used to be a burning question for me as well. I realize that looking for a reliable free proxy is always a challenge. Free proxies may not be as stable and secure, but if you choose wisely, you can find good options. Here, for example, this link has information about free proxy server that can be suitable for different purposes.
Started working with online platforms where you need a proxy server for anonymity and data protection. But, of course, I don't want to spend on expensive services, and free options are not always reliable. Does anyone have experience with free proxy servers and can advise how to choose a good option?