Hey! I just published an update for this pack that means it properly supports RTHandles and the Blitter API in URP. I've tested it and it is functional in 6.0.0 (and I believe by extension also 2023.x), however you do need to disable Render Graph to make it function.
It looks like the requirement to support Render Graph introduces another breaking change so I'll need to develop another update to support both RG and non-RG workflows. The non-RG workflow works with Snapshot Shaders Pro, though. I think Render Graph will be enabled by default in Unity 6 LTS, whenever that drops.
For now, you can disable Render Graph via Project Settings -> Graphics -> Pipeline Specific Settings -> URP. You will find a checkbox to disable Render Graph near the bottom of the window. It's not a perfect solution but I hope you can at least use these assets for now!