Existing adverbs are provided in this article. The words listed here are commonly found along with the verb existing in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb EXISTING.
absolutely, actually, apparently, barely, chiefly, concurrently, continuously
currently, entirely, eternally, exclusively, formerly, generally, immediately
independently, legally, mainly, merely, naturally, necessarily, objectively
originally, permanently, possibly, potentially, presently, previously, primarily
probably, really, separately, simply, simultaneously, solely, truly
usually
Hope this word list had the existing adverb you were looking for. In addition to adverbs used with existing, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.