Please see the double taxation treaty between the UK and Hong Kong. Article 14 suggests this income would remain taxable in Hong Kong. However, if you are a UK resident for tax purposes for the 2021/22 year then you are required to declare your worldwide income on a Self Assessment form.
Hong Kong: tax treaties
With regards to the MPF and if this qualifies for tax exemption, you would need to check if this is a qualified overseas pension by checking the recognised overseas pension schemes notification list:
Check the recognised overseas pension schemes notification list
Any further information on whether your pension scheme is a qualified one or not will need to be directed to our pension scheme services.
Once the facts are established this will allow you to decide if the gross or net of pension contritbutions figure is declared as your taxable income.