1: You're probably connecting to the terminal too late to catch the real boot menu. You only have 3 seconds from the moment it completes the bootloader download to the time it starts booting into the firmware. PuTTY is notorious for this issue. The wiki for this device currently has a link to the post with the instructions to recover to 23.05, which is what you need because the devices were never properly and completely converted to 24.10.
The good news here is that since it's booting into OpenWRT, this means its boot chain isn't corrupted; It's only confused by an incompatible firmware. That means you probably don't need mtk_uartboot to get to the boot menu and the steps for recovery. Connect the serial console cable and launch the terminal program before you power on the router. Make sure that if your terminal program has a setting like "local editing" such as what PuTTY does, that must be turned off. That setting prevents the program from sending anything to the router until you have completed a full line and hit Enter / Return. Since the boot menu requires entry of a single numeric key, that setting is incompatible.
Since you can get to the real boot menu here, you can recover to 23.05 simply by either launching the recovery environment from the boot menu or by writing a 23.05 sysupgrade over TFTP as the production firmware.
If all goes wrong, you can still follow the below to recover:
2: You've more or less done the same thing to this unit, too. That one word does indeed make a major difference. One is simply an initramfs image, and the other performs the conversion. If you never even get any LEDs, things have gone a bit more pear-shaped. You might still be able to access the real boot menu without the need for mtk_uartboot. If so, you can upload the correct (23.05) recovery image over TFTP following the instructions in the above-linked post.
Neither of these routers are properly running 24.10 yet, so they have to be treated as if they're still running 23.05. However, any time something like this happens, there's a risk of trouble. If the above instructions work, make sure you have the 5GHz radios working. If so, back up a copy of the factory partition. That data is all you really need in combination with the linked post to recover from any future firmware issues. If the 5GHz radio does not work, do not try to upgrade to 24.10. It means the factory data was damaged and must be replaced before you can perform the upgrade. Again, the linked post contains instructions on how to do this.