Why does this lines appear at the edge of the photo? only way to fix it is by cropping the photo.

I'm using a canon eos R3 with a Tamron 18-400. I also have that problem when I import into LR. I've discovered that by unchecking the remove chromatic aberration and enable lens correction boxes, no cropping is needed.  But those boxes being checked on import is a new problem. 

I've had the same problem with my 24-240 lens on a Canon R6 Mk2. It only started a few months ago. I then noticed Lightroom had introduced a new Profile for this lens in their later updates,visible by clicking the right end of the Profile box. I selected v2 rather than the latest v3 and  the fault disappeared. I made v2 the default.

All of a sudden, I started having this same issue. Not on all images in the beginning and then later more and more. I thought it might be the card, but previewing the CR file in Preview was fine. The jpeg too. So it seemed to be only happening after import. First I was cropping that part out. But later found out that turning the Lens Correction off, removes these lines. I'm using the 24-240 lens. 

I recognize this. Adobe's lens correction profiles for several iPhone cameras (especially the ultrawide cameras) when shooting raw in the Lightroom app are not well tuned and this causes this smearing at the edges. Indeed only fix is cropping. 

Edit: just remembered that an easier fix is to counteract the overcorrection of lens distortion in these files is to dial in manual lens distortion correction of -5:

Unfortunately Adobe does not allow one to turn off the built-in lens correction which would also fix this problem.

As others have indicated, more information is needed.

Another check, if this is a RAW image. is to look at the embedded JPG preview. I believe in most cases this can be done in your OS file manager/finder. If it is on the embedded JPG image, then it is likely a camera issue.

Just a thought out of the box, are you using a camera model that has the feature to automatically create a lens profile, with the option to turn the option off?

What camera (make and model) took this photo? Is it raw or JPG? What version of LrC? (we need the version number and not words like "current" or "up-to-date")

What happens if you turn off the GPU (Preferences->Performance tab->Use graphics processor set to OFF) ?

Is this shown on every picture?

Please check the appropriate picture(s) files in another viewer if there's seen the issue?

Try to use another memory card in your camera.

Check your camera.