Can't you use the verb on the infinitive in this case? something like "Diese Katze schwimmen sehr gern"? Is it wrong is any way? I get that schwimmt works fine but i wonder if there is a secondary way to structure this sentence
There are so many ways to say this. I think 'Die Katze liebt das Schwimmen' should be an option.
"The cat swims very well" should be the evglis translation to this
Imho that would be "Die Katze schwimmt sehr gut", whereas "Die Katze schwimmt sehr gern" means "The cat likes swimming very much".