Hey
The reason which Ninety One and most other brands have started putting components from other companies rather than Shimano is because of the scarcity of parts globally.
The pandemic has caused a crazy spurt in demand the world over. And bikes and parts are in short supply.
Which is why you are seeing other brand drivetrains make their way onto the bike.
Even if you go in search of Shimano components to change, you will likely have to change everything. There MIGHT NOT be cross compatibility between brands. Which means you need to buy derailleur and shifters from Shimano.
Which again depends on whether it is available. And at what price. And will that price be worth it?
Have you tried getting your existing gears checked and tuned by a competent mechanic?