TLDR: Debian will stop producing 32-bit iso installer images. You can still use 32-bit applications. This will stop you from installing the newest version of Debian on a 32-bit processor. That's all.
Yeah, I mean if you want to get picky, the actual i386 processor family hasn't been supported by the Linux kernel since 2012, and was dropped by Debian in 2007.
Most people were generally not particularly affected by that, seeing as the last i386 chip was released in (I think) 1989!
Debian's choice to refer to the whole x86-32 line as i386 has always been a weird historical quirk.