I get quite a few buy my cards to frame them. A recording studio manager bought a lot of my guitars to do that. My colour abstracts are often framed by customers.
I haven’t seen the final result, but guess that they just framed the card with the picture adhered, or, because a number have a border, maybe trimmed the picture on a trimmer to remove that border before framing.
As regards temporary fixing, transparent photo corners can suit landscape prints providing they are not too big. They would be visible of course, on the card. Maybe there’s a secret-fixing version available ?
Printed cards can be permanently fixed with good quality, double-sided tape.
I tried the acid-free variety, but is a lot more costly, and have monitored using both acid-free and some non acid-free versions over more than a couple of years, and can detect no difference at all in the images.
It may depend on the quality and thickness of printing paper and inks one uses, though. I don’t cut corners there, and assume you wouldn’t either.
You have to be careful to avoid overlapping the tape, otherwise it can show through the image. Spray adhesives can be used, but are messy, and tape is really fast if you have a proper dispenser.