Do you need it for a or just for fun?
Before providing any guide, it is critical to address the security risks associated with the specific version you mentioned. flash player v90246 offline download link
This ZIP file contains installers for multiple platforms (Windows, Mac, Linux) and specific builds within the v9 release cycle. Salesforce Installation Guide for Legacy Flash Player Do you need it for a or just for fun
If you must download, remember: verify signatures, disconnect from the internet, and never, ever use the browser plugin on a daily-driver machine. Salesforce Installation Guide for Legacy Flash Player If
has removed all official download links and strongly advises users to uninstall the software immediately to prevent security risks. Why You Should Avoid Offline Download Links
Only install v90246 on an offline, air-gapped virtual machine or a dedicated legacy PC that never connects to the internet.
Scammers prey on nostalgic users. Here is what a fake download looks like: