The CTR-baseline method
Pull your top 200 queries from GSC for the trailing 12 months and the trailing 90 days. For each query where impressions held but CTR dropped 30%+, an AIO is likely now appearing. This will not catch every AIO query but it surfaces the highest-impact ones.
Save the baseline as a benchmark and re-run monthly. The CTR drop pattern is the most reliable signal you can extract from GSC alone.
Why a dedicated filter does not exist yet
Google has been deliberately conservative about exposing AIO data in GSC, partly because the AIO product is still iterating rapidly and partly because the publisher pushback would be significant. A dedicated filter may eventually appear; in the meantime, the inferential methods above are what reasonable analysts use.