Generally you'll need an input of type file, and then either a button or link to call JavaScript and use the Portals Web API to upload it to a Notes record (or alternatively a file field on a specific record)
See the following links (for the last link read the whole post not just the tagged solution)
https://learn.microsoft.com/en-us/power-pages/configure/write-update-delete-operations#prerequisites
Fubar
69
Super User 2025 Season 1
oliver.rodrigues
49
Most Valuable Professional
Jon Unzueta
43