I have a Linksys WRT1900AC v1 mamba on version 19.07.3 and need to upgrade it to the latest supported version 23.05.4, link below.
I read other posts of users on 19.x having same error "mamba not supported by this image ....." due to the larger kernel space and change to DSA.
Is it safe to download the factory image from the link above, and use this command sysupgrade -F -n factory.img directly from 19.07.3 to 23.05.4?
yes, Linksys WRT is one of the few devices, were sysupgrade with factory image works and is required in some cases (factory instead of sysupgrade image is required in the special case of coming from Linksys WRT v19, to properly resize partitions)
but for practical reasons, I would nevertheless wait a few days and keep an eye on forum updates: at least for the larger Linksys WRT editions, people alerted defects in the Linksys WRT specific partition switching in some cases during firmware upgrade: Linksys WRT32x bricked both partitions.
I frankly do not know if the 1900 is also affected, but there is a chance that is partly affected as well.