Check out the official Asus support forums before you buy.
I got a ZenFone8 when it came out and was very satisfied with it at the time.
Then, a month later, posts started popping up with people reporting that their phones just randomly rebooting and bricking. I think there were a few hundred cases reported.
To this day, there is no official response from Asus.
I used to carry a backup phone with me every time I was away from home for longer than a day because I was afraid that my phone could die at any moment.
Also, every update seemed to introduce a new bug that only got fixed in a month or so with the next update. So we had broken face unlock for a month, broken Google Pay, broken notifications, among other things.
I haven't been following reports for the ZF9 or ZF10, but I think they had similar problems.
To top it all off, the official unlocker / root tool from ASUS has been disabled for over a year by now, and nobody knows when it will work again.
All in all, ASUS phones (at least the ZenFone line) do have great hardware, but official support is abysmal.