I think this might be caused by an update to Dynalist to respect the OS setting, as mentioned here.
This feature is actually pretty nice. However, it seems that they just check the OS mode and override the Default theme with the Dark theme. Since they didnāt keep the original Default theme as a separate Light theme which does not get overridden, it makes it impossible for users with dark OS mode to get the (old default) light Dynalist theme.
It shouldnāt be too difficult for them to add the Default theme as a separate Light theme option that doesnāt get overridden by the OS mode. @Erica seems to be pretty responsive, so I think theyāll realise and start fixing it soon, if they havenāt already.