For saving things you will probably want something different than excel, something like sqlite locally perhaps, or hosted versions like mySQL/mariaDB/postgreSQL/noSQL etc.

by "app" if you mean phone app and you are writing for apple products, I think swift is right.

if you want it to be "web" app then you can write in whatever backed language you want and have a lightweight platform specific or one of the generic framework to call api/view site on phones as app.

you have a lot of choices in everything. if you want a web app, I can recommend Node.js, express.js and postgreSQL -- not sure how to turn it into mobile app, but I am sure there are plenty of ways.

you could do it with excel I suppose (running machine with excel on it and connecting your backed to excel somehow etc), but it will probably be much more difficult and unsafe thing to do ----but maybe I am not familiar since I haven't seen mobile/web app built on top of excel before