Losing space in disc Ubuntu 20.04

I'd like to say what I think.

1. It is normal to use the browser and email client to bring some cache files. They need to cache some login information, pictures, videos and even some static files to speed up the access. This takes up some disk space.
2. It may be an automatic security update to the system that downloads some packages accidentally, but I recommend that you don't remove them without fully understanding them.

If you really want to clean up, there are many ways to do it online. For example: sudo apt autoremove removes packages that are no longer needed. You can also download specialized cleanup software, such as BleachBit

I think cache files, logs, and automatic updates and package downloads are the main reasons for your reduced free space.