Does it have anything to do with the number of inputs and outputs on the transaction window at all? It says 25 inputs and 1 output. Probably irrelevant, but I don't know what else to focus on. Like I said, this happened last month to me, and I simply updated my version of electrum, after which the coldcard read the psbt file.
Eh, that's actually the issue.
Coldcard supports 20 inputs to be signed at once[1], presumably due to the fact that it is unable to sign so many due to hardware limitations. I've never encountered this issue, only because I've never had to sign that many inputs but I think that the limitation still applies right now. Since it's mainly a hardware limitation, there isn't anything else that you can do other than to split the transaction up smaller.
[1]
https://github.com/Coldcard/firmware/blob/master/docs/limitations.md#max-transaction-size