Hello Akira Kakinuma

The best choices is 

1. taking 3 steps ( v.9.18.2 ⇒  v.9.24.3 ⇒  v.9.24.14 ⇒  v.10.12.9) 

And You can choice 

3. taking 1 step ( v.9.18.2 ⇒  v.10.12.9) ※v.9.24.31 is the newest ver.9

If you widgets and app store modules are supports with upgraded version 

Before doing any version to upgrade make sure that.

Hi Akira,

Please follow the documentation on: https://docs.mendix.com/refguide/upgrading-from-9-to-10/

In your case you first need to upgrade to 9.24.x and then to 10. But do check the documentation as it also lists other items to check.

Hi Akira,

   I would suggest strongly recommend following Option 1: v.9.18.2 ⇒ v.9.24.3 ⇒ v.9.24.14 ⇒ v.10.12.9 because we can found issues with deprecated widgets, modules, or functionalities can be addressed during intermediate versions (e.g., v.9.24.x), which offers better compatibility compared to directly upgrading to v.10.12.9.

Pro Tip:

         Create a New Branch: Before initiating the upgrade, create a separate branch for this process. Perform all upgrades and testing on this branch to keep your main line unaffected.

          Resolve Issues at Lower Versions: Use the intermediate versions (v.9.24.x) to fix deprecated or incompatible components. This way, your main branch remains stable, and the upgrade process is more seamless when merged back.

This method not only reduces risk but also ensures that the upgrade is thoroughly tested and stable before being deployed.

For more details please follow the document https://docs.mendix.com/refguide/upgrading-from-9-to-10/

Regards,

Guna