The phrase "although legally" is correct and usable in written English.
It can be used to introduce a contrast or exception related to legal matters or implications.
Example: "Although legally permissible, the action raised ethical concerns among the community."
Alternatives: "even if legally" or "despite being legal".
The marriage effectively fell apart soon afterward, although legally it lasted almost twenty years.
Although legally binding only in New York, the court decision potentially holds important implications for immigrants' rights nationwide.
Although legally unjustifiable, the witch killing has long served as a mechanism for rural villages to expunge antisocial behavior.
Middle-class parents are likely to be charged for an increasing number of services, and there are fears centres could face cuts in local authority funding now that the money councils get from the government is not ring-fenced – although, legally, they still have to provide sufficient centres to meet local needs.
Although, legally speaking, they have no right to vote on the new constitution, since it will be finalised before they formally join the Union next May, political reality gives each of them what amounts to a veto, since all their parliaments will have to ratify the new constitution.
Although, legally speaking, it may still be possible.
She lives as female, although remains legally male, perceiving herself as neither male nor female.
Although not legally binding, like a prenuptial agreement, it looks much better as wall art, especially now that artists are writing and illustrating them with increasing fancifulness.
Although not legally binding, the declaration was intended to serve as "a common standard of achievement for all peoples and all nations".
Although nothing legally binds a future mayor to spending money committed in the city's 10-year capital budget, cutting such funds would be politically costly.
