One thing you could do: FTS5 has the `fts5vocab` virtual table [1] that has all the terms. You could provide a user-defined function that computes the levenshtein distance between your query terms and the terms in that table, obtain candidate terms that way and build a big query that searches for all those lexically close terms.
[1] https://www.sqlite.org/fts5.html#the_fts5vocab_virtual_table...