The function marked in above images is returning wrong URL.
We are trying to upload from B website but this function is giving the URL of A (main) website to the Garavity form upload plugin.
I’m unable to replicate the issue in a default WordPress multisite installation with no other plugins active and using the default WP theme.
Based on our experience and the details of the issue I would recommend you to perform a full conflict test. Due to the nature of the issue, in this case you need to perform the conflict test manually, following all the steps described here: https://docs.gravityforms.com/testing-for-a-themeplugin-conflict/
Note that for a valid conflict test, as the documentation explains, the first try must be done with only Gravity Forms enabled, all other plugins disabled, and using a default WordPress theme without custom code (e.g. Twenty Twenty-One).
If you don’t feel comfortable doing this in the live site, you will want to create a staging clone for testing. I’m sure your host would be able to assist you with this task.