I do not know the reason but, finally I solved this problem with the way below:
First of all, it seems that there are local database files in "/Users/*/Library/Application Support/com.wizards.mtga" .
The error may happen because there are some incompatible json formats or like that. So, rename "/Users/*/Library/Application Support/com.wizards.mtga" to a another name like "bak".
Next, boot MTGA application from EPIC games launcher. I finally could run app and play the matches!
I saw the same error on MacOS X Sequoia.
I do not know the reason but, finally I solved this problem with the way below:
First of all, it seems that there are local database files in "/Users/*/Library/Application Support/com.wizards.mtga" .
The error may happen because there are some incompatible json formats or like that. So, rename "/Users/*/Library/Application Support/com.wizards.mtga" to a another name like "bak".
Next, boot MTGA application from EPIC games launcher. I finally could run app and play the matches!