@nubechecorre
There were 2 tools as replacement for the obsolete "Avail FLUSH":
expunge and flushlibs.
"Expunge" is in the SDK and using "Expunge ALL" should be similar to using "AVAIL FLUSH" in AmigaOS <= 3.9, but only regarding to unused libraries and devices, not for compacting memory pools for example, which are independent and incompatible implementations in AmigaOS <= 3.9 and AmigaOS 4.x.
"Flushlibs" may only be/have been available to AmigaOS 4.x beta testers, not sure anymore, but did the same as "Expunge ALL".
In AmigaOS <= 3.9 using "AVAIL FLUSH" could have been required to update unused, but still loaded in RAM, libraries in LIBS:.
AFAIK on AmigaOS 4.x that's not required anymore and automatically done with file change notifications.