Grist is a relational spreadsheet, available online or, as it is open-source, as a self-hosted docker stack.
Currently, n8n is able to connect to the online version of Grist but not to the self-hosted one.
Please allow connection to the self-hosted version of Grist.
Grist Labs have made the commitment to open-source their tool. One can expect that self hosted installations of Grist will multiply.
Here is the reference of Grist API.
Yes of course, as a tester