Mirokhodets

Well, there are sites that will help better than programs and vice versa.

1. Google Slides Free and quite convenient. Works in the browser and has mobile apps. However, this is a cloud service, so if you need a completely offline experience, it will not work.
2. OnlyOffice Presentation The free part of OnlyOffice includes a presentation editor. Can be used offline in a mobile app or desktop. The interface is more modern and convenient than Impress. Partially FOSS (client is open), you can disable the cloud.
3. Calligra Stage Part of Calligra Suite is a free office suite with a presentation editor. There are versions for Linux, Windows, but there are no official mobile clients. The interface may seem unusual, but the functionality is decent.
4. WPS Office (free version) Free office with presentation support. The interface is similar to MS Office, convenient and modern. Not fully FOSS, but free and works offline.
5. Deckset (for macOS, paid) A very convenient tool for creating presentations based on Markdown. There is no free alternative on Android, but this is an example of the approach.
6. Marp Markdown-based presentations. Free, cross-platform (there is an Electron version). It requires a little getting used to Markdown, but it is very flexible and convenient for those who like the text approach.

LibreOffice Viewer — The official LibreOffice viewer, available for Android. True, it mostly only has viewing and very basic editing. But it's native and offline.

OnlyOffice (standalone version is optional) — There's an Android app that can be used offline, with support for major formats (DOCX, XLSX, PPTX). Although the software is not fully FOSS, the client is open, the server can be stored. Collabora works better on mobile devices.

OpenDocument Reader/Editor — Less well known, but a simple ODT rider and editor, you can search for it in F-Droid. Very lightweight and offline.

AndrOpen Office — A port of Apache OpenOffice to Android, fully offline and FOSS. The interface is old-fashioned, but the functionality is decent.

Why did you write as if I insulted Linux?

Probably each school has its own approach

Here, to be honest, there is some truth, since the phone is more convenient and you can be anywhere with it. BUT this does not mean that the PC is crap, since even when doing firmware on the phone, you can simply be left without it (turn it into a brick), but on the PC you can run ANY DEVICE, including a phone.

I don't know about others, but I only have 2 emails, one with Google Mail and the other with Proton Mail.