https://www.sentinelone.com/blog/what-happened-to-my-mac-app...
> Last week, just after we covered the release of Big Sur, many macOS users around the world experienced something unprecedented on the platform: a widespread outage of an obscure Apple service caused users worldwide to be unable to launch 3rd party applications.
> As was well-documented over the weekend, trustd employs a “fail-soft” call to Apple’s OCSP service: If the service is unavailable or the device itself is offline, trustd (to put it simply) goes ahead and “trusts” the app.
Even at the time people quickly figured out you could just disconnect from the internet as a workaround until the issue was fixed.
Perhaps you turned some "make things ultra-secure" setting on at some point ?
It used to be that you could run any third-party application you downloaded. And then for a while you'd have to right-click and select Open the first time you ran an application you'd downloaded, and then click through a confirmation prompt. And macOS 15, you have to attempt to open the application, be told it is unsafe, and then manually approve it via system settings.
You can't distribute software through the Apple or Microsoft app stores without the software being signed.
You can sign and distribute software yourself without having anything to do with the app stores of either platform, although getting a signing certificate that Windows will accept is more expensive for the little guys than getting a signing certificate that Macs will accept.
This is just Gatekeeper asking you which code-signing CA certs you want to mark as trusted in its kernel-internal trust store (which is, FYI, a separate thing from the OS trust store): do you want just the App Store CA to be trusted? Or do you also want the Apple Developer Program's "Self-Published App" Notarization CA to be trusted?
Choosing which code-signing CA-certs to trust will, obviously, determine which code-signed binaries pass certificate validation. Just like choosing which TLS CAs to trust, determines which websites pass certificate validation.
Code-signing certificate validation doesn't happen online, though. Just like TLS certificate validation doesn't happen online. It's just a check that the cert you have has a signing path back to some CA cert in the local trust store.
This warning only triggers for legacy releases of apps, published before notarization existed. Since Catalina, notarization has been part-and-parcel of the same flow that gets the self-published app bundle code-signed by Apple. AFAIK it is no longer possible to create a code-signed but non-notarized app bundle through XCode. (It's probably still possible by invoking `codesign` directly, and third-party build systems might still be doing that... but they really shouldn't be! They've had years to change at this point! Catalina was 2019!)
Thus, the "Open anyway" option in this dialog is likely transitional. This warning is, for now, intended to not overly frighten regular users, while also indicating to developers (esp. the developer of the app) that they should really get out a new, notarized release of their app, because maybe, one day, this non-notarized release of the app won't be considered acceptable by Gatekeeper any more.
I'm guessing that once a sufficient percentage of apps have been notarized, such that macOS instrumentation reports this dialog being rarely triggered, the "Open anyway" option will be removed, and the dialog will merge back into the non-code-signed-app version of the dialog that only has "Cancel" and "Move to Trash" options. Though maybe in this instance, the dialog would have the additional text "Please contact the app developer for a newer release of this app" (because, unlike with an invalid digital signature, macOS wouldn't assume the app is infected with malware per se, but rather just that it might do low-level things [like calling private OS frameworks] that Apple doesn't permit notarized apps to do.)
Also, a CRL/OCSP check isn't a gating check — i.e. it doesn't "fail safe" by disallowing execution if the check doesn't go through. (If it did, you wouldn't be able to run anything without an internet connection!) Instead, these checks can pass, fail, or error out; and erroring out is the same as passing. (Or rather, technically, erroring out falls back to the last cached verification state, even if it's expired; but if there is no previous verification state — e.g. if it's your first time running third-party app and you're doing so offline — then the fallback-to-the-fallback is allowing the app to run.)
Remember that CRLs/OCSP function as blacklists, not whitelists — they don't ask the question "is this certificate still valid?", but rather "has anyone specifically invalidated this certificate?" It is by default assumed that no, nobody has invalidated the certificate.