If what you are looking for should be similar to the fuzzy / free-form search for documents, but on workflows, then there is no such functionality in Alfresco. There is support for basic database-oriented lookup / selection in the APIs, but none of those are directly exposed in the user interface - and even if they were, they only support very basic exact match / pattern-based matching.
What I have done in an experiment years ago (ca 2012/2013) was to create a "virtual node" service which mapped workflow and task instances to virtual Alfresco nodes, and then used Alfresco's regular indexing and search capabilities to query them. E.g. where a regular node would have workspace://SpacesStore/xxxx-xxxx-xxxxxxxx-xxxx like structure, the workflow / task instances would be workflow://Activiti/xxxxxx (using the DB ID + a number pattern to provide a stable identifier length unless you had billions of instances).
But this was quite an excessive / intensive customisation, and AFAIK changes to Alfresco core since then likely would prevent a similar approach from working nowadays.
