Car shakes and gives alarm signals when driving on higher shifts/faster?

Hello, (I can't edit the car mileage, I marked it in kilometers! My car has 100,000 km! Not miles)
My car listed above is a IV, 1.2 TCE 130. With an electric turbo.
So, I've owned this car now for about two years. I've had the maintenance done by professionals yearly. Every once in a while the car signals a low level of oil even though the oil is fine (I check and my finance checks).
The oil was last changed in June.
The oil light came on once again about a month ago, but the level seemed perfectly fine so to be honest we ignored the sign (we did keep checking the oil at least once to two times a week)..
My fiancé was driving the car on the highway when all of a sudden it started making sounds, lighting up all kinds of alarms (including the little motor sign which to my understanding means that the toxic fume filter / antipollution needs to be checked, saying to check the injection etc, basically everything starts lighting up one by one) and the car shakes like crazy.
He manages to get it carefully home and we take it to a mechanic. He changed all four sparkplugs because when checking them he said the part that goes in the motor was disgusting, and most likely one of the roots of the shaking he also said the oil level had dropped drastically low meaning it had dropped within a week from last check immensely and he had to add a lot of oil. This did help a bit and we have been using now only 98 gas in the car which has also improved the situations since the car doesn't shake st all when going on low speed and low shifts. We can hear the electric turbo activating normally, the car clearly gets some assist from it when pressing on the gas and all is fine, the only thing I would say the car still expects you to get on slightly higher RPM before shifting gears than before but that's it. The real problem arises when driving on higher RPM and shifting to higher gears (4, 5 &6). The car shakes more and after a few minutes, it signals the antipollution, injection etc one by one and starts shaking a lot more. It also seems to struggle to get to higher RPM s and just over all feels like at has no "power". If you then slow down the car keeps being shaky even on lower speeds and shifts, but, if you stop the car, let it rest for about 30min-1hour and start again, the problem is gone on the lower shifts (will start again if you have to go above 40-50km/h).
I am planning on using an engine and cylinder cleaner this week and maybe even doing an oil change because I believe in June they put a low-quality oil, maybe even a wrong viscosity.
But, what do you think could cause all this? Any tips and ideas? We are obviously not driving with it right now just in case it's actual damage in the engine (God I hope not). I am planning on taking the car to am official Renault mechanic, but I would like to be a bit more prepared for it, knowing a bit what to ask to check for etc. This is my first slightly more expensive car I've ever owned and I am completely broken up about this. I've taken good care of this car, I truly am not an idiot with it. My poor naive brain still hopes it could just be a small thing to fix (like an electrical problem or maybe that the turbo is malfunctioning in an easy to fix way). Any tips or ideas you could have are greatly appreciated! Thank you