Hi, Please find the difference below,

Computed:

A Computed field can be simply defined as a field for which the value is computed using a method rather than directly reading from the user. This may be a Basic field or Relational field with an additional attribute ‘compute’ within the field definition. Consider a business model to manage Rental orders, where the total rent amount is calculated from the duration and price for the unit duration. For this purpose let us define a monetary field total_rent  as in the following code which is a computed field where the value of this field is computed using the value of another field or more than one field.

Depends:

The Depends function depends(*args) returns a decorator that specifies the field dependencies of a “compute” function. For the depends() decorator each argument must be a string and it is also possible to pass a single method as an argument. In such cases, the dependencies are set by calling the defined method.

For more information refer the blog:

https://www.cybrosys.com/blog/difference-between-compute-and-onchange-fields-odoo

Hope it helps