That is a warning that the next version of macOS or maybe a future version will not run 32 bit software.
Apple hasn't really made it clear as to what the timeline for actually not be able to run 32 bit apps is.
As long as you stay with macOS High Sierra 10.13, pse 8 will run just as always.
It's only if you upgrade to macOS 10.14 or whatever the next version is called that you'll not be able to use pse 8, possibly.
If you do decide to upgrade then there is no update for pse 8 to make it 64 bits, but you can upgrade to pse 2018 or whatever the current elements version is at that time and it will be a 64 bit application.
Unless you find some compelling reason to upgrade to macOS 10.14, there is no reason to hurry up and do it, since High Sierra will be getting security updates for a few more years, at least.
Of note is that apple says according to
Apple prepares macOS users for discontinuation of 32-bit app support | Ars Technica
To prepare for a future release of macOS in which 32-bit software will no longer run without compromise, starting in macOS High Sierra 10.13.4, a user is notified on the launch of an app that depends on 32-bit software. The alert appears only once per app.
What does 32-bit software will no longer run without compromise mean?
and also
The next release of macOS after High Sierra will begin to restrict 32-bit apps and will feature "aggressive" warnings about the coming change. Apple has not said at exactly which point support will be phased out completely.
what apple writes
32-bit app compatibility with macOS High Sierra 10.13.4 - Apple Support
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