Hi Ras,
It would help if you posted a picture of what you're seeing on the screen, but chances are high that you do indeed need a new screen.
I can't be positive, but I'd say it's very likely your fingerprint reader will work again once you've put a new screen on. If not, the good news is the actual reader itself can also be replaced if need be. Regardless, all of your issues with cracks and lines will be resolved with replacing the display. iFixit doesn't have a guide for your phone, but there's a Spanish site called Nadie Me Llama Gallina that has just what you need.
Manuales / Samsung Galaxy A71 / Fullscreen
You can get replacement parts on many different sites; I usually start with Amazon, eBay and AliExpress, but there are lots of others to choose from. Here's an example.
Amazon.com: YWLRONG for Samsung Galaxy A71 Screen Replacement Display Touch Screen Digitizer LCD for Samsung A71 A715F SM-A715F/DS SM-A715F/DSN A715FD Display Repair Part(Black with Frame) : Cell Phones & Accessories
Good luck with your repair; let us know how it goes!
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I have these white vertical lines as well on my screen, and increasing almost daily. No physical damage, phone was not dropped. Problem started after recent software upgrade...
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