it wont let me download microsoft remote desktop

Hello, sash823.

How to Upgrade  macOS:

The macOS version you can upgrade to depends on the model and year of your Mac. Click the  (Apple) menu at the top left of your screen and choose About This Mac. 

❗️ – IMPORTANT – Backup your data. (You’ve been warned.)

Learn How to Back up your Mac with Time Machine:

https://support.apple.com/en-us/HT201250

❗️ – IMPORTANT – Your 32-bit apps won’t work in Catalina or Big Sur.

Use this free utility to check the compatibility of your apps:

St. Claire Software – Go64: https://www.stclairsoft.com/Go64/

🖥 – Check compatibility of your Mac with newer versions of macOS.

https://support.apple.com/en-us/HT201475

✅ - Using Safari only, download the macOS upgrade installer:

Click > Mojave, Catalina or Big Sur.

Did you download Remote Desktop v10.6.7 from the Mac App Store or another source? Verify from menu > About This Mac that you really do have macOS 10.14.6 or later installed. I know that Remote Desktop states 10.14 or later, but Microsoft has released a flurry of updates for this application in recent months, and it may be pickier and expect the last Mojave update.