I have avast! free 19.8.2393 (build 19.8.4793.544)
Whilst, Avast had the intention of a monthly program update cycle, it isn’t hard and fast that it will be monthly. There have been other things going on that have had a greater priority. There has been a beta release for avast 19.9.2394 (build 19.9.4824) https://forum.avast.com/index.php?topic=229911.0 and that would certainly come first before any regular program update. But so far that hasn’t been released from beta testing.
Reboot if you haven’t done so recently.
The 541 - 544 build would be considered a very minor update and may probably have been delivered in a VPS & Engine update.
If a reboot doesn’t do it try a manual program update followed by a reboot.
Actually I’ve been doing that many times earlier, and it’s still .541 since weeks already. My AV still says it’s up to date (and no new updates available) even when I try to manual update. I don’t actually care about it much as long as it works, but still I’m wondering why some have newer version and I have older. Only Virus Definitions are updating.