I've been using
Total LHM Plus hydraulic mineral oil for years.
Used it with a lot of Shimano and Magura brakes. Both disc, and hydraulic rim brakes. Haven't noticed any problems with seals, or performance.
It costs about 1/4 of the Shimano oil price. Not sure about Magura's "Royal Blood" - shops here don't have that in stock.
Unlike baby oil, this oil is designed for that purpose - but it's not sold as "bicycle" brake fluid.