How can I get a hardcopy (2020) SE user manual?l

You can only find an iPhone manual as a bookmark in Safari on your iPhone, or as a free download in the Books app on the iPhone. From Books, you may have the option to print individual pages, but they have stopped with printed manuals to keep them up to date easier. Just like computer software companies have done. They have their manuals online as well, so you get the most up to date info, and you don't have to download help files like we used to back in the day. You can go to this link as well, iPhone User Guide - Apple Support User guides are by iOS now, and all phones that support that iOS are listed inside.

Apple - Support - Manuals

Print it out yourself.

Went to link referenced and there is no SE 2020 manual there.

The iPhone user manual is based on the iOS version and not the phone model. Tap on the link for iPhone iOS 13 guide.