touchscreen does not work

Has anything happened to the phone recently, such as a drop, liquid exposure, firmware update, etc.?

Your phone actually has two separate digitizers; one for your finger, and one for the S-Pen. If one fails, often the other will continue working; I had a Note 4 where the S-Pen digitizer failed but the touch screen still worked.

Anyway, assuming it's a hardware failure, the cause is almost always the digitizer rather than a problem with the motherboard. The fix is to replace the entire screen, as you can't really replace those three components separately, at least not without very specialized equipment and expertise.

So you'll want to try all the software fixes you can come up with first, such as hard resets, doing a backup and full restore, etc., to make sure it's a hardware problem. After that, you'll need to replace the screen. Here's the iFixit guide to doing that on your phone.

Samsung Galaxy Note10+ Screen Replacement - iFixit Repair Guide

Unfortunately, your phone is still fairly new and prices for a new screen haven't come down a lot, so it's going to be somewhat expensive to fix. You can buy a new screen right here on iFixit, and it appears to be available in other markets such as Amazon, eBay and AliExpress.

Galaxy Note10+ Screen

If you buy it from iFixit, I recommend the Fix Kit, as it comes with all of the tools and adhesives needed to do the job right for a minimal cost.

Good luck; let us know what you find!