Correct, you basically either need to upgrade to Windows 10 or Linux. If you really want to mine with Windows 7 then you need to use the blockchain drivers. I tried on a rig and it worked as intended. Basically modded the bios with Pimp my Straps and used the -rxboost and -install option on Claymore and got I think 28.75MH/s using 1126/1950. All with a slight undervolt.

This is only on a rig with 2 GPUs, if you got more than 4 GPUs then you got no choice but to upgrade because from what I recall you can't use more than 4 GPUs. There was a fix for this during the Litecoin mining days of 2014 where you installed a patch, however that patch only worked with older GPUs like R9 280X. Reason why is because it only patched an old AMD drivers version from like 2015, the newer ones were never patched since most people just used Win 10 to mine.

Also support for Win 7 is running out next year, so there will be no more security updates. Its crazy but the OS is already 10 years old.