Hello, if someone doesn’t get it, here’s the solution.

Enable two-factor authentication (2FA):

Go to https://myaccount.google.com/security.

Under Google Sign In, find and click Two-Step Verification.

Follow the instructions to enable two-step verification. You will need to add a phone number to receive codes.

Create an application password:

After enabling two-factor authentication, go to https://myaccount.google.com/apppasswords.

Create a password for the Mail application. It will look like a set of 16 characters.

Set up Dekko 2 using the application password (16 characters):

Open the Dekko 2 app on your Ubuntu Touch device. Proceed to add a new account and enter your Gmail email address. When asked for a password, use the generated app password instead of the normal password from your Google account.

IMAP and SMTP server settings:
IMAP server: imap.gmail.com
IMAP port: 993
IMAP encryption: SSL/TLS
SMTP server: smtp.gmail.com
SMTP port: 465 or 587
SMTP encryption: SSL/TLS

Two days of torment and I finally managed to do it.

@pauloaugusto Great your up and running and yes I am using the first sim slot too. Not sure that the dual sim works on any device yet.