I had the opportunity to test this today, and I can confirm that the firmware updater for the web interface with scock firmwar version1.1.00.015 does indeed accept the 'factory' image file for OpenWrt 23.05-RC1.
I started with firmware v.1.0.00.010 and it appeared to accept the image (it said it was successful and then rebooted), but it did not reboot into OpenWrt. Since I didn't have the time to crack open the case and setup a serial connection, I found the download for 1.1.00.015 and installed that -- my next attempt flashing OpenWrt was fully succesful.
Interestingly, it was rather hard to find the .015 version of the firmware -- it is mentioned on the Linksys support page, but the only firmware I could find there was 1.1.00.033 (both signed and unsigned). I wasn't sure if the newer firmware would still accept OpenWrt, and the support article also states that downgrading is not supported (I don't know if there updater will simply not accept an old image, or if there is a risk of bricking the unit, or if it is just not 'supported' but would work... I didn't feel like testing it). I did finally find version 1.1.00.015 on the Linksys Korea site.