turns out it needs at least two rdc files to crash the client. I tried it once again with just one in the first collection and undid that without the client crashing. but as soon as I created a second collection and imported the second rdc file into that and undid that the client crashed instantly.

rdc files are quite large in file size (~40 MB each), I doubt this form will accept such big files.
yes, it's unofficial. it is the Maps Model Importer from Elie Michel (https://github.com/eliemichel/MapsModelsImporter).

to create an rdc file you need two other tools:

• RenderDoc to inject into the GPU process of Google Chrome (https://renderdoc.org/)
• Google Chrome to capture a Google Maps area in the 3D mode via the RenderDoc interface

Here's a video on how the rdc file capture process is done:
https://www.youtube.com/watch?v=F_XsmoZJmG8

the thing is I don't know whether it is the undo function that is responsible for the crash or the addon.

This form will accept those files. I don't have time tinkering with tools to capture maps really.

There is statement on https://github.com/eliemichel/MapsModelsImporter/releases

This add-on requires specific versions of Blender, Chrome and RenderDoc. You can try with other versions but please try these before reporting an issue.

Perhaps it would be good to report bug on addon tracker first to see if this is really bug in Blender. It's developer may be also able to provide more detailed info as well.

I have attached two example rdc files onto this post as requested.