How do one knows he is filing in old or new tax regime for the assessment year 23-24

Hi, I logged in and just about efiling the income tax for the above assessment year. Suddenly I came to know of old tax and new tax regime.

Is the default efling for the assessment year 23-24 on old tax regime

If it is not, how do i choose the old tax regime. Can I change the tax regime before submitting the online form

Is there any easy way of knowing if I am filing in old tax or new tax regime please tell

Should we make a temp calculation of tax in old and new regime before opting for old or new

Is there any link that i could use the income on both the systems and choose before going to efiling portal