ANSYS Student 2021 R1 is no longer available.

You can download the latest version, which is ANSYS 2022 R2, that has a Built-in license valid until 07/31/2023.

You can download the two Prior versions, which are 2022 R1 and 2021 R2.1 that have a Built-in license valid until 01/31/2023.

If you check Prior versions in 2023, you will find you can download a fresh copy of 2022 R2 and its built-in license will have a new expiration date. That is the only way to get an extra six or so months on a specific version, but once 2022 R2 drops off the list of the two Prior versions, you will not be able to get a new expiration date.