If you're ever in Australia, save yourself the effort and don't come out to where I am, it's an utter hole.

Although the Great Ocean Road is nice, and there are some pretty towns out in the regions. Daylesford is pretty popular, though I'd planned to go there and had to cancel due to lockdown and never rescheduled so I can't give a proper recommendation. It's a hot springs town and prides itself on its inclusivity, definitely a plus. If you're into hiking there is the Grampians National Park/Gariwerd which is closer to where I am but I would stay in Dunkeld before Hamilton tbh, much nicer place.
I do recommend Melbourne more than Sydney but I have been living in Victoria a while so I have that bias. Great food, galleries, sports (more of a me thing granted). NGV and ACMI are must sees for art and/or history nerds. Brisbane and the Gold Coast are great for theme parks and more of your beachy summery holiday though. Probably recommend the Sunshine Coast instead, however, as it's a little less touristy and a bit more chill, at least as far as I remember.
It's funny though, I find when you live somewhere long enough it gets hard to recommend any sort of touristy things because it all just becomes a bit mundane. I always had that problem when people visited Brisbane, never knew what to recommend. When I visited my ex in Canada I think he had the same problem, we didn't do very much in the way of sightseeing.
I've started going on tours though because I'm having a mid life crisis. Probably don't get as much of a local insight/only really see the super touristy stuff but as an anxious solo traveller it's been pretty good, feels pretty safe and gives some guidance and suggestion. I went to Japan last year and I'm going again with a friend soon so I'm dragging him to Hiroshima for a day, I genuinely think that's somewhere you
must see in Japan, particularly if you have even a passing interest in history. Also going to Universal Studios and I'll try not to think about the price while I'm there.

Will let you know how I go with it and with South Africa on another tour later on!