Rather than using specialist greetings card software, I simply use a desktop publishing program, adding my own photographs or graphics found on the web via a Google Images search.
For example, for my Christmas cards this year, I put one of Woodelf's paintings on the front of a card, positioning it at the bottom of an A4 sheet. Then I put the image and text for the back of the card at the top of the sheet, rotating it by 180 degrees so that when folded across the middle it will be the right way up:
https://ibb.co/Y7q0Qp8
(Click on the image to enlarge it)
I printed the card outers onto normal A4 glossy photo paper.
I used some pictures of my cats for the insides of the card, putting everything into the top half of an A4 sheet and then duplicating it all onto the bottom half:
https://ibb.co/VBp3mcK
I printed the composite sheets onto two-to-a-sheet sticky labels
https://www.a4labels.com/en-gb/white-address-labels-200-x-144mm
thus overcoming the problem of printing onto the back of photo paper.
I then used standard C5 envelopes to post my cards.
(As examples of cards that I created solely using graphics found on the web, here's the front of a Christmas card from an earlier year
https://ibb.co/PNwK1F2 and here's the outer for a card I made for a cat-loving young friend's 12th birthday
https://ibb.co/gPCbTPb )
The DTP software I use (Serif PagePlus X7) is no longer on the market but any decent DTP program should be able to do the job. (Scribus, which is a freebie, is an obvious choice here:
https://www.scribus.net/ )
Alternatively consider using an online card creation service such as Adobe Creative Cloud Express
https://www.adobe.com/express/create/card
or Canva
https://www.canva.com/create/cards/greeting-cards/