This question would be more suitable to ask on firebird-devel. See
https://firebirdsql.org/en/mailing-lists/ (under "Firebird Developers'
Lab") for details how to subscribe.
That said, I'm not aware of plans for a Windows ARM64 build, the only
ARM64 build that exists today - AFAIK - is the Android build.
Contributions to create *and* maintain such a build are always welcome,
but discussion on that should be done on firebird-devel.
Mark
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Mark Rotteveel