I found a solution for QuadHD monitor and M1 Mac and posted on Macrumors forum. Search "Solution. QuadHD monitor with HiDPI and Mac Mini M1" in Google. Briefly, you need to buy 4K HDMI EDID emulator (8 USD), USB-C to DisplayPort or HDMI converter (8-12 USD) and enable Mirror Displays option in macOS. Now you'll see scaled HiDPI resolutions.

Thanks, Matt!

Thanks for your reply! It would be helpful if Apple could show several learning videos (or just screenshots) with examples how our apps look at a normal window size and in fullscreen mode with different modes. I think that many macOS developers have the same question now.

It shows a lack of information for software developers. I didn't find any official info how to implement 120 Hz ProMotion support in my macOS app.

I have a similar strange problem. Today I discovered that I cannot longer notarize my macOS app (outside AppStore): "Error: You must first sign the relevant contracts online. (1048)". I tried on 3 Macs, no VPN. I check developer.apple.com > App Store Connect > Agreements, Tax, and Banking. I see updated License Agreement. But I cannot sign it. There is no sign or accept button! Why? I'm a holder and admin of this Apple ID for our small team. I tried in Safari and Chrome.

I contacted with Apple support. And they manually approved the updated contract. Now I can notarize macOS apps.

I found a solution. I use QuadHD monitor with Mac Mini M1, but macOS doesn't support HighDPI on this monitor. Fonts small & sharp or large & blurry. So I use Better Dummy free utility which emulates secondary 4K monitor and use mirroring to use HighDPI 2560x1440 on this display. Visual artefacts appear after screen lock or sleep. When I disabled this utility to use native non-Retina resolution the problem didn't appear. I found "Disconnect and reconnect after sleep” option in this utility and it helped to solve that problem. However it can be a bug in macOS.

Thanks, I'll try this.

It seems that Apple solved this problem in macOS 13 Ventura. I checked Beta 6 today and it offers several HiDPI resolutions for my external display Dell 24" QuadHD (2560x1440) connected to Mac mini M1. No need to use BetterDummy utility or dummy 4K HDMI emulator.

Hi Quinn, Thanks for your fast reply and suggested solution. I will keep using spctl command, because use of a clean VM is very complicated. Why Apple cannot simply modify Gatekeeper to add a special mode for developers for testing apps? In this special mode any caching would not be used. I believe that building a software package should be fully automated to save time of developers.

Hi Quinn, Thanks for your reply. My app is not sandboxed. I tried another idea. The old app copies own APP bundle from Applications to Application Support > MyAppFolder. And tries to run it (as an agent to perform the Auto Update). The same problem - the copied APP gets com.apple.quarantine attribute and cannot be launched.

Quinn, Can I use another approach? Create a small APP bundle (Auto Update utility), not sandboxed. Include this utility to resources of main product APP bundle. Old APP copies this small APP utility to Application Support > MyAppFolderSettings Run small APP utility. Launched small APP utility deletes еру old APP bundle in Applications. And copies a new APP bundle to Applications (downloaded and extracted in Application Support > MyAppFolderSettings folder).

I raise this question again. Earlier you suggested: "The easiest way to do this is use Xcode’s import/export feature. Launch Xcode, choose Xcode > Settings, select Accounts, select the account in question, then choose Export Apple ID and Code Signing Assets from the action (…) menu." In Xcode 16 I cannot find any import/export commands to move existing codesign certificates/keys to my second Mac. Probably it will easier to create a NEW individual codesign certificate for EVERY Mac I use?

Hi Quinn, Thanks for your reply. I use "Developer ID Application" certificate. So I've read your recommended article: https://developer.apple.com/forums/thread/732320 If I understood you rightly, you suggested to create 2 independent "Developer ID Application" certificates/keys for 2 my Macs with the same Apple ID account? I've read your mentition that 5 certificates are maximum allowed. In another source I've read that once I create new certificate, it will deactivate other existing certificates. Also on Apple Developer website I can only download created certificates and cannot delete unused certificates. I mistakenly created one more certificate which wass not used. Note, that your article still contain a mention of export/import features in Xcode which are no longer available in current V16: "Alternatively, Xcode has a feature to export and import your developer account, including your Developer ID signing identities. <...>"

Quinn, Thanks again for your reply. Sorry, I'm still confused, please can you write a separate chapter with an instruction how to copy existing "Developer ID" certificate/key to second Mac?