The phrase "although not compulsory" is correct and usable in written English.
It can be used to indicate that something is optional or not required, often in formal or academic contexts.
Example: "Participation in the workshop is encouraged, although not compulsory for course credit."
Alternatives: "though not mandatory" or "even if not required".
Although not compulsory under World Trade Organisation guidelines, the EU has chosen to abide by the lesser-duty rule, which restricts punitive tariffs on dumped goods.
Although not compulsory, monitoring of patient doses and comparisons to national values are routinely recommended [41] and perhaps mandatory reporting of CT doses within the diagnostic report would increase the use of this important optimisation tool.
Although not compulsory, certification allows patients to be registered (ie, placed on an official local council register) as either severely sight impaired (blind) or sight impaired (partially sighted), which then permits access to certain state benefits and social service provisions.
Although not compulsory, you will almost definitely be expected to help with housework in your new home.
Although chickens have no visible teeth, they can hurt when they peck, so gloves are a welcome option although not compulsory.
While some canon characters have vague pasts that can be manipulated, a frequent and recognized (although not compulsory) trait of a Mary Sue is to be related in some way to a canon, especially one who has a strongly established past already.
Schools in Spain are free from age four, although schooling is not compulsory until age six.
Although attendance was not compulsory, conservatives viewed the mere existence of girls' schools as an offense against basic morality.
Although voting is not compulsory, the participation rate is high, with about three-fourths of eligible voters casting ballots.
One state school working to ensure that does not happen is Hove Park School in Brighton and Hove where, although languages are not compulsory, 92% of pupils took a GCSE in one this year.
A spokeswoman for the company confirmed that airport store teams are asked to request and scan boarding cards to ensure the "accurate reporting of VAT", although this was not compulsory.
