Indirect disposal of non-residential property by non-resident company

BVI Co. A wholly owns BVI Co. B for over 10 years, and B is dormant since incorporation. B bought one UK commercial property in 2016 with total purchase cost of GBP5million (including stamp duty and other incidental costs) and earned rental income solely throughout the years. No other acquisitions / asset / business in B after 2016 acquisition.
In 2024, A sold entire shares of B to third parties with an agreed property value of GBP4.1million making the total consideration of GBP4million. GBP4million includes share consideration of GBP1million and repayment of B's loan GBP3million. Market Value of the UK commercial property is GBP3.8million on the sale date. B is property rich asset. For the calculation of A's gain/loss on indirect disposal of UK land, what is the correct disposal proceeds and relevant tax base cost?
I am quite confused with the below link.
Thank you very much.
https://www.gov.uk/guidance/capital-gains-tax-for-non-residents-calculating-taxable-gain-or-loss?gad_source=1&gclid=CjwKCAjw68K4BhAuEiwAylp3kqn4_C3wFJra3tHK1HjbRGW7gboju9fatuezeXKg_dLAgbzd6q8ikRoCPPgQAvD_BwE

Hi,
This forum is for general queries only and is intended to help you self-serve. 
HMRC cannot give tax planning advice which is the category your question falls into.
Guidance is available at Businesses and as already quoted by you at:
Work out your tax if you're a non-resident selling UK property or land
You will need to determine what action you need to take after consulting the guidance or engaging a financial advisor/accountant to assist.
Please refrain from posting the same question multiple times on this Forum and await the answer to the first question posed.  
Thank you.