Are you saying your iPhone 11 is now working by disabling wi-fi and leaving wifi disabled while on bluetooth? Or saying this step works on a 7S which is not the thread issue....this is an all iPhone 11 issue thread.
No matter, disabling wi-fi to make Bluetooth work is an unacceptable workaround.
I had an iphone 7, and the same Bluetooth devices, multiple earbuds v4.x , my 2016 toyota tundra entertainment, all worked just fine with the iphone 7. and at the latest IOS version ( as I just bought the new iPhone 11). I will note my bluetooth v5.x earpiece had issues on iphone 7 also. Not the v4.x devices. Supposedly the iPhone 11 should work with Bluetooth v5.x.
This for me is exclusively iPhone 11 issue at latest IOS and the thread is aptly name 'iPhone 11 Bluetooth issues'.
None of the fixes/steps mentioned by Apple support have worked, and I have tried them (reset network for example). It is clear as day an iPhone 11 issue.
Glad your 7s is working though I wish same for my 1200 iPhone 11!