The original PROJ library supports the General Oblique Transformation projection (+proj=ob_tran)
https://proj.org/operations/projections/ob_tran.html

I would like to use this same projection in Proj4js.

I pay 1000 euros for someone to implement it.
https://www.upwork.com/jobs/~01dbbbfa2519110a46