You could complete your text requirements on screen and then use the Windows Snipping Tool (or Snip and Sketch in Windows 10) to save what you've created as a jpeg image. (i.e. your text would then be a 'photo'). You could then upload that 'photo' to any card production company that allows you to just use a photo without any text (as your own text will then be part of your 'photo').
For example, Funky Pigeon offer such a service here:
https://www.funkypigeon.com/card/full-photo-no-text-portrait-card-basic/10391
Photobox (where the cards are sent to you, for you to sign and post, rather than despatched to the recipient directly as with Funky Pigeon)have a 'blank card' option here:
https://www.photobox.co.uk/shop/cards/single-cards
However Woofgang's solution seems easier (and cheaper) to me. I design all my greetings cards in a DTP program but, if you only require text, word processing software would be as easy to use. I then print them onto A4 glossy photo paper, ready to be folded into two, thus creating A5 cards. As you can't print onto the back of photo paper, I print the inner parts of the cards onto A5 stickers, which I then stick inside the cards. (Ryman sell them:
https://www.ryman.co.uk/ryman-universal-labels-200x143mm ). C5 envelopes (to hold A5 cards) are widely available from discount stores, supermarkets and office stationers.