I would suggest plugging the vehicle into a battery maintainer when performing an update. Otherwise, you will have to idle the vehicle for up to 30 minutes while the software is downloading. The battery will run down if the software update is attempted in accessory mode.

 

My software in my 2019 OdyEX is B.1.3.4. Anyone knows if this is the latest update?

 

B1.3.4 is the latest for 2019.

2019 Honda Odyssey Over the Air System Updates

2019 Honda Odyssey Over the Air System Updates: Software Versions: B.1.0.21 B.1.0.26 F021 B.1.3.4 FDC17.05.005/NAD 200.0.9A00 and B.1.4.4 AOT10738 2019 Odyssey: Software Update Display Audio/Navigation Available Applies To: 2019 Odyssey - EX, EX-RES, Touring, Elite - ALL - FCB...

www.odyclub.com

 

A battery maintainer isn't necessary.
The software update can take up to 30 minutes. If you don't have a battery maintainer, then I would idle the vehicle during the update.

 

how to know what is the last version for 2020 EXL?

 

I think you go to settings and look for 'about ' and it'll show your software version.