Yes! “Consider topics new if I haven’t viewed them yet” has some built in safeguards to avoid trading in enormously expensive queries.
In particular:
We allow for max_new_topics total on the site.
https://github.com/discourse/discourse/blob/master/config/site_settings.yml#L1163-L1166
This is a hidden site setting which is hardcoded to 500. We can probably bump it up on your site a bit, but it risks introducing performance problems.