Mit MacOS Mojave will probably be the last Mac operating system released, which can also start 32-bit programs. Already under High Sierra one is already pointed out to this circumstance, if one starts such an application. If you are unsure whether you have apps that have not yet been optimized for 64-bit, then you can easily verify this. We'll show you how to tell if an application has already been optimized.
How to Check Your Mac for 32-Bit Apps
Click on the Apple logo in the top left corner, and then choose About This Mac. A new window will open with information about your Mac, click on "System Report ...". Another window will open all sorts of technical details now. In the left sidebar, under Software, select Programs. Depending on the system and the number of applications installed, it may take a moment to get information on the right side. At the top right you will see all installed applications in alphabetical order.
Drag the window further to reveal more columns. Underneath is the "64-bit (Intel)" column, which indicates whether the application is already optimized for the 64-bit architecture. Clicking on the column header sorts the applications for assistance, giving you a quick overview of all 32-bit apps. These are named "No" in the "64-bit (Intel)" column.