Upgrade Web Site to PHP Version 8.5

My site, https://gbrainsinfotech.com/, is still running on PHP 7.3. I want the entire installation — core files, any themes, and every plugin or custom snippet — migrated to PHP 8.5 with zero loss of functionality and no visible downtime.

I am not sure whether custom scripts are hiding in the codebase, and I do not currently have a staging setup. I therefore expect you to check the repository thoroughly, spin up a safe clone for testing, and flag any incompatibilities before the live push.

Deliverables
• Staging environment created and shared with me for review
• Code and database upgraded to PHP 8.5, including any refactors for deprecated functions
• Full functional test covering pages, forms, login areas, and anything else you identify during the audit
• Final deployment to production with rollback plan documented

NOTE:- After Final Review in Go Daddy account PHP version has to updated.

Please outline the number of days you need and your fee in INR, along with any assumptions you are making so that I can approve the scope quickly.