How to re-do 1960's type hollow core doors?

You can redo them but you need to sand lightly to get any sheen off, clean thoroughly, prime with a good primer such as Zinsser Bullseye 1-2-3 primer and then your final coat or coats.

This site has some great ideas on how to make hollow core doors look like expensive doors.

https://www.schlage.com/blog/categories/2015/03/how-to-make-your-hollow-core-doors-look-expensive.html

https://www.hometalk.com/diy/windows-doors/doors/hollow-core-bore-to-a-beautiful-updated-door-diy-slab-door-makeover-15862926?expand_all_questions=1

I have one in my kitchen & hate it. Neighbor came over saying she painted hers with black “magnetic paint” (never heard of it). Sure enough, she has notes & all the stuff we stick on our fridges...I’m gonna try.

use picture molding from the big box stores - . There are so many styles that you can any to compliment your style.

Paint and put on molding to make it look like raised panels

You don't say if they have been painted before or are wood veneer. You could always add a trim or trims (double sided tape) and then paint.......

Get them in the ground !

My house came with these and I dislike them too. Best choice is to replace them with new doors, which is what I did. There are a few tools required and development of skills to use them properly. I used solid core doors, but hollow core six-panel colonial door slabs are available for around $40 each. You'll need store-bought jigs and chisels to inset the hinges and a kit to drill for the latch.

If you decide to just paint, use a semi-gloss or gloss paint, following the advice given by others for surface preparation. Check out Pinterest for ideas on how you can customize paint scheme or adding molding to suit your taste.

What other Hometalkers have done.

https://www.hometalk.com/search/posts?filter=hollw%20core%20doors

Here you go:

https://www.hometalk.com/posts/repair/windows/adding-trim-to-doors-3062128