Windows 10 Shift + Arrow Down

Both those functions work on my Edge and IE11 no problem. I suspect you have either windows corruption or virus/malware infection. The first thing to do is try to rollback your W10 using the built-in SYSTEM RESTORE to a point in time before the problem began to appear. That works some of the time, maybe 1 in 4. If it does, you're computer is fixed and you're good to go!

If the problem persists; we recommend you scan with whatever your AV is you have installed on the computer and scan/remove all found viruses. Retest for the problem. If it does, you're computer is fixed and you're good to go!

If the problem persists, next check for spyware viruses using the free MALWAREBYTES from malwarebytes.org. scan/remove all found spyware viruses. Retest for the problem. If it does, you're computer is fixed and you're good to go!

If the problem persists, you might have further windows corruption caused by non-virus/malware sources, or failing or failed hardware. In either case you need to determine which is the case, so the best way to do this is to test your hardware. Then apply increasingly more aggressive software solutions until you repair it up to and including W10 reinstallation. If you fail to test your hardware 1st, the software may repair the problem temporarily, but it will reappear in hours/days/weeks/months if the real cause is hardware failure.

I wrote a very helpful Troubleshooting Guide which will provide you with step-by-step instructions on how to test your hardware and repair or reinstall ;W10--which 99% of the time will fix your problem assuming your hardware tested Ok or if components failed you replaced them with brand new ones.
Here's the link to my Guide: Windows 10 - Unclickable Task Bar

Post back if you have any problems with the Guide troubleshooting.
Best of luck,
<<<BIGBEARJEDI>>>