Actually wide tables for example can't be done at all.
And technically we can use Microsoft Excel as a photo editor. But that's just ridiculous. Just like it's ridiculous to say you can use relational models for any data structure even if the queries will never return.
You are still missing the point. The relational model is not about particular implementations. There is no limit on number of columns etc. It is not "ridiculous to say you can use relational models for any data structure", it is the whole point. That particular implementations may not suite your requirements is not a problem of the model, it is a problem of the particular implementations.
There may be other limitations, but MSSQL supports[1]:
Columns per nonwide table 1,024
Columns per wide table 30,000
I think a lot of this RDBMs can't do X, came from using a MySQL. It has improved some, but was garbage until recently.
I'm not sure how wide you're taking about, but PG support up to 1600 depending on the datatypes (there is a page size maximum). Oracle supports 1000 IIRC.
As I recall, MonetDB claims "practically unlimited" number of columns per table. And in this particular use case you're probably looking for an RDBMS specialized in analytics, not a general-purpose one like Postgres. But relational model will handle it certainly better than any other.
And technically we can use Microsoft Excel as a photo editor. But that's just ridiculous. Just like it's ridiculous to say you can use relational models for any data structure even if the queries will never return.