What version of flutter is required?

[PopeNobody]

3.251 
3.251 The lower bound of "sdk: '>=2.0.0-dev.68.0 <3.0.0'" must be 2.12.0 or higher to enable null safety.
3.251 For details, see https://dart.dev/null-safety

This is odd. According to flutters release page they went right from 2.10 to 3 ... so what is this 2.12 of which you speak?

[PopeNobody]

9.129 9.140 Running "flutter pub get" in flutter_tools... 4.9s 14.15 Running "flutter pub get" in oxen-wallet...
16.85 The current Dart SDK version is 2.16.2. 16.85 16.85 Because flutter_slidable 2.0.0 requires SDK version >=2.17.0 <3.0.0 and no versions of flutter_slidable match >2.0.0 <3.0.0, flutter_slidable ^2.0.0 is forbidden. 16.85 So, because oxen_wallet depends on flutter_slidable ^2.0.0, version solving failed. 16.88 pub get failed (1; So, because oxen_wallet depends on flutter_slidable ^2.0.0, version solving failed.)

I can rule that one out.

But here are more versions.