EDIT: Apologies. Updated with a link to what gorhill REALLY said:
Manifest v2 uBO will not be automatically replaced by Manifest v3 uBOL[ight]. uBOL is too different from uBO for it to silently replace uBO – you will have to explicitly make a choice as to which extension should replace uBO according to your own prerogatives.
Ultimately whether uBOL is an acceptable alternative to uBO is up to you, it’s not a choice that will be made for you.
Will development of uBO continue? Yes, there are other browsers which are not deprecating Manifest v2, e.g. Firefox.
And jump to the clone? Mozilla isn’t better (consider their recent Ad Privacy clone), they just have less market share.
That said, I use Firefox and Brave. Whatever I feel like at the time.
The clone? Are you implying that mozilla (founded 1998) is a clone of chrome (first launched 2008)?
Just use anything but chome or chromium if you can. Just don’t feed the beast now known as alphabet.
There are plenty of browsers built on Gecko that aren’t fire fox. So if you don’t trust Mozilla to build your browser, and don’t want your ad blocker bricked by Google, you have options.