Can a builder extend the RERA deadline date?

I have make 95 % payment to the builder till dec 2021 and as per agreement possession to be provided by May 2023. Till date builder has not provides possession and told us that they will provide possession by Feb 2024 as Rera has given them extension during covid *Now I want to know that is rera extension affect date of completion.* Further as per agreement one clause says that all cost is including applicable taxes and duties for example 50 lacs and another clause which was added by builder in the model agreement that GST would be paid extra . *In this case is extra GST i.e 50 lacs plus GST has to be paid by me.*