AI files exporting to very low PNG quality only (2019 vs 2021 version)

I started using Illustrator in 2019 and would “export as” numerous basic AI files to very high-quality PNG files, quick and easily, all the time.

Then at the end of 2020 I upgrade to a new iMac (because the new 2020 version of Illustrator would not install on the dinosaur iMAC version I was using). I now use iMac macOS Big Sur Version 11.2 and Illustrator 25.0.1

However, since I upgraded my Mac and Illustrator, all the Illustrator AI files export with very poor quality. I have tried to find a solution online, looking at others who posted a similar issue but, so far, I could not find the answer to my problem.

Attached is a copy of: (the post would not let me attach a copy of the AI file - I can email a copy if it would help find an answer)

• a copy of the “Export as” png file I originally exported in 2019 (quick, easy, high quality)
• a copy of that same “Export as” png file when I exported it today, in 2021 (low quality, not usable, waste of time)
• a copy of the file exported today using “Export from screen Artboard” (also low quality)
• a copy of the file exported today using “Save for Web” (also low quality).

Right now, I don’t see the point of using Illustrator if this is the quality of the product it exports. It should not be this difficult to work out.

If someone could please tell me a way to export my AI files to high quality PNG it would be much appreciated.