My understanding is that Catalina will no longer be able to execute 32 bit binaries.
It isn't that clear whether they just mean Carbon 32 bit binaries (which pscan isn't) or whether they mean all 32 bit binaries including "unix" and X11 (which pscan is, which is why it needs XQuartz to run).
After some coding and configuring of compilers it seems possible to recompile pscan as a 64 bit X11 app, and I have now tested it on an old 10.6.3 (Snow Leopard) laptop and on a Macbook Pro 8,3 running 10.13.6 (High Sierra). I don't have access to a Macbook that will run a newer version of OSX than that.
pscan0426 is now available for upgrade and is a 64 bit binary.
pscanloader downloaded before 6th Oct 2019 is a 32 bit binary, but when you run it will run the 64 bit pscan app.
If you wish to upgrade pscanloader to 64 bit as well (and it might be that Catalina will force you to) then you can download the 64 bit version from
http://pscan.uk/download/macosx/pscan.uk.dmg
as described at
http://pscan.uk/install/macosx.html
.
I would appreciate it if folks with Macbooks could test the 64 version (including the new pscanloader if possible). It would be better to test it now so that if there are problems then I can just roll back to the 32 bit version whilst this is still viable. Once Catalina is deployed this might not be possible.
Also if people have Mojave then feedback would be useful as I don't have it.