@v-monli-msft Attachment upload IS supported in portals.
@Catherin You might be missing few steps to enable notes.
You should check below things:
1. In entity form settings, have you enabled the attachment options?
Refer to image A
2. In the actual form, have you set the activities default tab as notes?
Go to form designer -> Switch to classic -> Notes control properties -> In web client properties, set default tab as notes
[refer to image B]
3. Setup the entity form metadata for notes.
You can find the link here: https://docs.microsoft.com/en-us/dynamics365/portals/configure-notes
[The screenshots are of legacy webclient but it is same for UCI aka model driven app as well]
You can also refer to Image C attached
4. Now, most important step, have you provided appropriate permission to the webrole on notes entity?
For eg. If you want to enable attachment to the authenticated users, create an entity permission record, choose entity as notes, set the appropriate permissions here. That is referred in documentation above.
Do let me know if you have any more questions or does it solve the problem for you.
