Major browser vendors have disabled Flash Player from running, however, if you are using an old browser like Microsoft Internet Explorer (IE), or you have apps that require IE you may run into issues.
Adobe will not be issuing any security patches or Flash Player updates. If Flash Player was manually installed it can remain on your system unless it is uninstalled.
As related to vSphere Web Client, you will not be able to access vCenter to mange older VMware installations.
If you have questions about this Adobe Flash bulletin, contact Systems Engineering at info@systemsengineering.com, or 888.624.6737. Customers, please reach out to your Account Manager.