The problem with op24 is, while it is built on OWRT 24.x & uses the OWRT F/OSS WLAN modules/drivers, it still uses the GL GUI... but the problem isn't actually the GUI; it's all the custom scripts GL adds 'under the hood' to make that GUI function (case in point: the new PBR feature changes dnsmasq behavior). You might as well just run pure OWRT 24.02.
The critical detail to know is when flashing 'pure' OWRT is to only use the sysupgrade tagged releases. You should have no trouble flashing it via the GL GUI. It's the bootimg version puts one at risk of bricking the device. Do not use bootimg.
It's trivial to flash back to GL firmware using the 'U-boot WebGUI'. See the link below. If you can set up Proxmox you have more than enough skill to flip back & forth between firmware as desired. Just don't mix up your backup tarballs. Here's a script to help quickly make backups. You can pull them down via SFTP (opkg update && opkg install openssh-sftp-server).