Shift key doesn't work on the letter I/letter I and K

Open up your System Preferences > Keyboard, then click on the Input Sources tab. Now click on the Show Input menu in menu bar so you have a way to check the keyboard. Also check the keyboard input in the left column you should see your language as an example I have U.S. for english.

Now open the keyboard viewer like I’ve done here

I had enabled the Caps Lock. Does your keys all change correctly?

When both the SHIFT key, and the I and K keys are working fine on their own, it means that the circuit of the keys printed on the foil inside the welded assembly is fine. (That is a part that is close to impossible to open and put together again.) I had a similar issue with left CMD + Z, X, C, V, B. Each worked on their own, but not together. I opened the keyboard and cleaned the ribbon cable endings as well as the connectors using contact cleaner fluid. It fixed the issue.

I assume that due to oxidation at the ribbon connector, certain electrical resistance builds up over time, and it can cause multiple simultaneous key presses hard to detect by the logic board. By cleaning these contacts, and some luck, the keyboard may be fixable. All you have to take care of to not bend it during prying it open. Use heat and be patient.

Once done and tested, put the front and back together in the right position, put the whole keyboard on a flat surface face down, and step on it barefoot a good few times trying to go around and apply pressure to all parts a few times. This way I managed to stick it back together using the original adhesive. It is perfect now.