I left the UK before 31 December 2020. Can I apply for pre-settled status from abroad to return to the UK?

You can apply for pre-settled status from abroad if you have lived in the UK at least a day in the 6 months preceding 31 December 2020. You will need to show you entered the UK before 31 December 2020 and provide evidence you were in the UK at least 1 day in the 6 months preceding this cut-off point. If you eventually want to apply for full settled status, you will also need to be very careful with your absences, and make sure you have not been away for more than six months since the last date you were in the UK before 31 December 2020 - since this will break your continuity of residence. Applying from abroad is very similar to applying from the UK and the information can be found here: https://www.gov.uk/guidance/eu-settlement-scheme-applying-from-outside-the-uk