It's called a calendar entry. Not every life experience is some giant challenge waiting for a tech bro to create a dedicated fucking app.

I can't reply to your reply so in case you see this:

Yes anything booked ahead I generally put into a calendar entry. iOS/macOS makes this pretty simple (it detects most booking emails and offers to create an entry for me; in those scenarios it has a link in the calendar entry back to the mail message). For the ones I have to create manually I just put any important info (e.g. confirmation/reservation codes) into the Calendar entry's notes field.

For things like boarding passes I don't think I've ever seen them delivered by email. Airlines like Thai and Singapore offer digital boarding passes via their mobile app, and they just import straight into iOS Wallet. I would assume there is some similar integration with a wallet-like app on Android.