What do you use to track down initial issues?

What do you use on your product to find initial problems, or how do you try to track down problems with users? For example, I opened my product to 20 random people, but first I installed Heatmap (Hotjar). After a couple of days, I saw that the users interacted in the right way - but for some there was a problem with the login, and since the login is required to use the main functionality, they left the product. After that, I added a login button in places where "You need to login" prompts are called - now it looks like "You need to login! (Login button)" What methods do you use? share your opinion)