This is an race issue, cause the form is still being evaluated while its being submitted, and the necessary resources are being created. Moving to Low severity, since its not effecting the install form.
Checked on ocp 4.10 with payload 4.10.0-0.nightly-2021-09-16-212009. 1. Navigate to Operators- OperatorHub 2. Install ODF operator 3. While installing, observe the UI, there is no error message "Subscription already exists in openshift-storage namespace" now.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Moderate: OpenShift Container Platform 4.10.3 security update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2022:0056