I still have my Early 2009 MacBook for my kids. It runs El Capitan and Windows 7 (bootcamp). Since the support for Windows 7 ended on January 14 2020 an upgrade was needed. Unfortunately the bootcamp 3 that comes with El Capitan doesn’t support any version higher.

Image from The Verge

A quick search on internet learned that upgrading Windows 7 to Windows 10 was easy. Just download the Media Creation Tool and download the bootcamp 4 zip for the updated drivers.

After 3 hours my old MacBook was running Windows 10 with the correct drivers. In the references all downloads are linked. The youtube link makes it dummy proof.
Maybe upgrading to macOS Catalina next time …

References

• Dual-Boot Windows 10 on An Unsupported Mac (youtube) – I only did the Windows 10 part
• Windows 10 Media Creation Tool – downloadable from Windows machine only
• Bootcamp 4.0.4033 (site:rebyte.me) or Bootcamp4.0.4033.zip (google)
• macOS Catalina Patcher – to upgrade unsupported macs