OK, since you’re getting the certificate error, let’s see if we can do this, as mentioned in the other post:
- Open the terminal and type
sudo nano /etc/apt/sources.list and enter your passcode. (This opens a system file that you’ll edit from the terminal.)
- On the keyboard, click on the globe icon and choose “Terminal” which will reveal some keys you’ll need.
- Using the down-arrow key, scroll through the displayed text until you’re positioned on the lines that contain links with “https:” in them.
- Navigating with the arrow keys, delete the s so that only “http:” is left. (Use backspace or delete, depending on where your cursor is positioned.) Change all the https to http. MAKE SURE you don’t change anything else.
- Finally, tap the “Control” key on the keyboard - it’s sticky - followed by the “x” key to exit.
- Confirm save, and save as same name.
- Tap on Control key to unstick it.
Now, with WiFi on, exit the terminal, go to the PureOS store, and select the Updates tab. Hit the refresh icon, and then approve any updates.
At some point, you’ll want to repeat this process to add the s back to “https:”, once the certificates get sorted out.