Hello people, spent the all day struggling with this issue. Only double click worked. Bought a mouse. Called Apple support and got a $370 service estimation. Didn’t go to Apple Store because couldn’t find any open. After trying everything checked the trackpad setting and found the option ‘tap to click’ - tap with one finger was unchecked due to my refusal to update macOS I guess. Just saying. But definitely I was ‘forced’ to update my MacBook due to this double/one click issue. Good luck 🍀