64 Bit apps
When will the conversion from 32 bit apps to 64 bit for MacOS High Sierra10.13.4 be completed?
I keep getting messages on screen when attempting to use certain apps.
There is no "conversion". MacOS is a 64 bit OS. Beginning with Catalina, this fall, it will no longer support 32 bit apps at all. So long as you don't update to Catalina, you have nothing to be concerned about.
If you are currently using 32 bit apps and want to upgrade in the fall, you will have to check with the developers to see if you can upgrade to 64 bit versions or find alternatives.