I have the same problem. Someone online said that you could do the upgrade with zigbee2mqtt but I looked into setting that up, and I think i need a separate coordinator dongle… so I am jjust stuck.
I wanted to say thanks and confirm that this solution worked for me, and I did successfully update my Thirdreality 3RCB01057Z ZL1 Smart Bulbs from version 20 to version 38 while on HA 2025.3.2.
I was glad not to have to go through the effort of switching from ZHA to zigbee2mqtt. Though, it took over 2 hours to update my first bulb. Perhaps my Zigbee network is less than optimal LOL.
Just out of curiosity… ZHA knew about my Thirdreality 3RSP02028BZ Smart Plug Gen2 and updated those firmwares automatically, I was on HA 2024.11 or so when I got those.
At some point, could we expect for this method to update the ZL1 bulbs be incorporated into some future version of ZHA hardware database, so it will automatically know how to do these firmware updates without issuing the manual action?