Unfortunately, I don’t know a way around it. I would bug ASUS support about it. Maybe if enough people care, it will eventually change. Supposedly they were gonna do it at the end of October. That obviously never happened.
Personally, I think the device should still be on the list. There is a caveat on the installation instructions page about the bootloader. If you manage to find a device where the bootloader is unlocked already, /e/ will still install and run fine.
It sucks that you can’t unlock the bootloader anymore, but that was a change from ASUS, not /e/. A similar situation exists with some Galaxy S7 submodels. The US versions of the phone can’t have the bootloader unlocked for some reason, but it works with versions sold in other countries. Again, it’s stupid, but that’s a Samsung issue, rather than an /e/ one.
It is so a shame, as it was the last hope for normal phone and not a shovel when it comes to the size. I was tricked the same way, shortly after buying Asus Zenfone 8 they locked unlocking bootloader. I contacted their support many times. They kept answering that they will return this possibility on autumn. In the end I have changed phone in November and now I would not recommend to invest in Asus phones. Nevertheless they produce great computers which can run Linux smoothly 