Microsoft retired SHA-1 support. Modern drivers are signed with SHA-256 certificates. A fresh install of Windows 7 (even with Service Pack 1) does not natively trust these certificates.
Using or NTLite , inject network drivers directly into the Windows 7 WIM image. This is advanced, but it guarantees that your system will have networking immediately after Windows setup completes. network adapter driver windows 7 offline installer best
Here is useful text regarding finding and installing the best network adapter drivers for Windows 7 offline. Microsoft retired SHA-1 support
If you are working with a pre-built machine (HP, Dell, Lenovo), the manufacturer’s support page is the gold standard. network adapter driver windows 7 offline installer best