You are confounding Income Tax and Capital Gains tax.
These are two completely separate taxes and you can not offset them one against the other.
Income Tax is a tax on your income (duh!) and includes tax on your rental profit as well as your PAYE income. To calculate your rental profit you deduct some, but not all, expenses relating to the rented property from your gross rental income.
The capital loss on the sale of the property, is not offset against your income tax. A portion of the loss can be carried forward to be offset against any future capital gains you might have. As the property was owned for 14 years and was your PPR for 6 of them, you will be able to carry forward about half of the capital loss (6 years as PPR plus 1 year = 7 years out of the 14 or 50% )
Provisional tax is a prepayment of income tax - it can be 100% of previous year's tax or 90% of tax actually due for 2021 (if you can calculate/estimate that in November 2021)