Airdrop - which allows you to easily transfer files between Apple devices, requires a Mac from 2012 onwards.
Using an iPad as a second display.
If you get the MBP the Touch Bar (some love it, but I hate it)
The ability to run any iOS App that the developer has allowed Mac OS access to.
Your current MBP has very slow connectivity, only USB 2, FireWire 1. So very slow transfer of data to external drives.
No Touch ID.
No ability to unlock your laptop with Apple Watch.
Most importantly, the performance of the M1 MBP will be light and day compared to your current MBP, instant on as you open the lid, super fast loading of Apps. As well as no fan noise and insane battery life.
Given that your 2009 MBP is sufficient then to be honest, save some cash and get the base M1 MBA, you don’t need the MBP. For your use case it will be just as fast as the more expensive MBP.
If you want to spend more and wait for the 16” MBP it is likely to have a new design with smaller bezel, but also likely to cost significantly more than the current 13” MBP.