I'm a big fan of spreadsheets for tracking stuff. I keep a Google sheet for each car to track spending and maintenance. Here's a copy of my 2014 Mazda 6 sheet. I track date, odometer, cost, type, and description. Type lets me categorize spending into a pivot table in a 2nd sheet, and do some arithmetic to figure out price per mile, and price per month over time. I've used Google Sheets as a default because that's where I started. I used a Google Form to make mobile input friendly, but went back to the mobile app for offline and faster access.
After the early demise of my iPhone 13 mini, I started fresh and didn't reinstall my previous apps. So I decided to give Numbers a try. I exported the Google Sheet as an Excel file and had no trouble opening it on Mac, and saving it to iCloud. On phones, there's "Enter data using forms in Numbers on iPhone". Each column can be customized with a type so "cost" can be currency and show the numbers keyboard, and "type" can be a pop up menu with a set list of options. It even imported the pivot table properly!
Sharing is available through iCloud web, and has familiar permissions and options. I also like the option to share as PDF. With Shortcuts, I added a "Record Mazda" shortcut that uses the "Add 'Values' to 'Form' in '2014 Mazda6 Touring'" Numbers task, and saved this Shortcut to my homescreen with a red car icon.