Legally, no. Monopolies do not generally need to aid their competitors to the point that they produce viable products. At times, however, monopolies do provide token support to competitors to reduce the risk of anti-trust enforcement. See, for example, Microsoft supporting Apple in the 1990s and Google supporting Mozilla.

Definitionally, companies without viable competitors are monopolies. Microsoft still has a defacto monopoly on PC operating systems as Linux isn't a viable choice for 95%+ of PC users. This market situation is extremely detrimental to consumers but isn't illegal.