My solo fantasy-ant-farming league is so niche that no one is
interested in talking about it.
niche (adj.)
Denoting products, services, or interests that appeal to a small,
specialized section of the population.
The video game industry is no longer niche Lexico
Denoting or relating to a product, service, etc., that occupies or
exploits a niche in the business world (see sense A. 4c); as niche
market, niche player, niche product, etc. Hence more generally:
narrow or specialized in scope or appeal; exclusive.
1978 Chem. Week (Nexis) 6 Dec. (Management section) 45 The thrust of Uniroyal's growth in chemicals and plastic materials is
development of ‘niche’ products. (OED)

As the domain of use for niche has expanded, so has its utility
as a modifier. Perhaps the use of niche in a figurative sense
coincided with its use as an adjective and its potential for
application to domains outside of architecture and ecology, not in a
causative way, but in a way that suggests it is speakers' use of words
that determines meaning and grammatical category (not the other way
around). A. Burkette and W. Kretzschmar Jr.; Exploring Linguistic
Science (2018)
Google Ngram:
