It’s literally: click the paper clip logo in Gmail, tap files, pick your file.

You can also just go into the files app, tap and hold, tap copy, go to Gmail tap and hold in your draft email, tap paste.

There’s other paths that work too, like hitting the “send to” logo in files and then selecting Gmail.

It’s really the exact same patterns I might use on a computer for the most part.

Google will often convert it to a gdrive thing instead. So you're not sending the file, just a link to the file uploaded somewhere. I'm not sure what heuristic it uses, but sometimes when mailing photos like half of them are included in the mail and half automagically uploaded to gdrive instead.

Thanks. I saw Photos and Drive, and apparently I missed "Attachments".

Still, copy-pasting a file should work. It's unclear what "copy" even does.