How long will it take for yeast culture to adapt to new flour
1:


  How long will it take for yeast culture to adapt to new flour


Starter will adapt to the new flour ratio with 3-5 feeds (if you feed it daily, it should change to the new flour within 7 days).



2:


  Is my starter slowly dying? Or just getting used to the new flour? If so how long will this take?


Add some rye or wholewheat flour for a couple of feeds.
If you wish to add white flour - that should increase the gas pockets in your starter.

I'd give it three to four feeds before you see some hyper activity.

The thing is - depending on your temperature - the starter should be active the closer its is to ~30C.

I'd say, unless there's pink spots or or mould, then you should give up.

Re: Giving up: can be checked in this other starter question.
https://cooking.stackexchange.com/a/107641/83535