some questions about migration assistant

When using Migration Assistant, it will indeed transfer all of your applications, including your old 32-bit apps, over to your new iMac. However, newer macOS versions, starting from Catalina, no longer support 32-bit applications, so they won't be able to run. This could result in some unnecessary clutter on your new machine.

Now, about your query on choosing specific apps to migrate, I'm afraid Migration Assistant doesn't allow you to select individual applications for transfer. It's more of an all-or-nothing deal when it comes to apps. If you decide not to transfer apps, yes, your keychain, along with other data and settings, will still be transferred.

For a cleaner start, you might want to consider manually installing the apps you need on your new iMac and transferring only user data and settings. This will let you avoid any potential issues with incompatible apps and will save you some storage space. Alternatively, you could transfer everything over and then uninstall the apps you no longer need. Just make sure to fully delete these apps to clear out the associated files.

I'd recommend going through these Apple Support articles to get a better understanding:

- Use the Migration Assistant to move data to your new Mac

- How to open a Mac app from an unidentified developer

- How to delete apps on your Mac

One thing to consider if you migrate your app with before or after upgrading you won't have to enter all of the license or activity codes for them.

If you don't migrate the apps make sure you record all of the activation data for the app.

You may want to go through the list of 32-bit applications that you have now, to figure out if there are any that you need to upgrade/replace (e.g., productivity applications that you use every day), as opposed to ones that you hate to lose (e.g., games).

To do this, select "About This Mac" in the Apple () menu. Click on the "System Report…" button. Then click on the "Applications" item (under "Software" in the side bar), and wait. When the Mac finishes making the list, click on the 64-bit (Intel) column header to sort the list by that attribute (and thus group the 32-bit ones together, for easier identification).

Also, to see which Apps will no longer work in 10.15 & upwards get Go64...

https://www.stclairsoft.com/Go64/