Is it compulsory to share form 12B with new employer? When do I will have to submit?

Hi, I have switched to the new company recently 20 May 2023. When do I will have to submit form 12B to new employer?
When will my old employer have to share form 12B with me? Is it compulsory to share form 12B with new employer?

There are a number of forms available under different laws relevant to employment. Therefore, while posting a query, it is advisable when you ask about any form, mention under which Act.

If you mean Form 12B of the Income Tax Act, I would say that it is not mandatory to furnish the same in the same legal or prescribed format but a declaration of income from past employment during the current financial year and TDS effected on it may be submitted to the new employer so that the latter can decide the tax slab and how much TDS be deducted from your salary every month.