You're right that things have gotten peculiar, to say the least, in the Add-Ons manager, but you can still access things if you have a bit of "inside info."
After I open the Add-Ons Manager:
1. Make sure you're on the Extensions control in the main control bar. If not then up/down arrow until it's selected and activated.
2. Hit TAB five times. Oddly enough, in my case, when I land on the Add-Ons list the first word out of NVDA's mouth is "Chrome." Why on earth that would be I have no idea. You can silence NVDA at any point after you know that you're on the list. If you let NVDA keep speaking it mentions heading level 2.
3. At this juncture hitting TAB takes you into the Add-Ons list. What's interesting is that the Add-On name itself is not what's announced, but the descriptive text for that Add-On. Since this often includes the name of the Add-On, it tends to be pretty clear, but not always. For instance, my DuckDuckGo add-on does not include that in its descriptive text, but instead they describe it starting with the word "Privacy." After the descriptive text if you TAB once you will land on what NVDA announces simply as button. If you activate that button a dropdown menu appears that you can down arrow through that includes Disable, Remove, Report and More Options.
4. Hitting TAB without activating the button takes you to your next add-on's descriptive text and another TAB to that add-on's "menu control button." Lather, rinse, repeat.
I hope the above is enough to allow you to get in and remove or disable what you want to.
Brian - Windows 10 Pro, 64-Bit, Version 1903, Build 18362
The color of truth is grey.
~ André Gide