I'd say it's an abomination that Quickbooks hasn't fixed this yet BTW, but in case it helps any other poor souls out there at the mercy of Intuit's ineptitude, the steps and solutions I've seen mentioned didn't work for me. The only one that finally got IE to actually activate again for me was Step 4 on this list from Microsoft: 

https://docs.microsoft.com/en-us/troubleshoot/browsers/disable-internet-explorer-windows