Anki will pick an ID higher than the current highest one. If you remove all cards with the high IDs, new cards will be added normally. The high IDs may have been added by third party software in the past.
But I found that when I created(added) one note with two cards at the same time,
one id was 13 digits but another was 15 digits (can see in linked GitHub image)
Yes, that is normal - it only uses the max+1 when two cards would have the same id.
Thank you for your answer.
I just tried manually removing the first two digits of the 15-digits ID (because an Addon requires 13-digits ID) in table cards-id and table revlog-cid
then i reopened Anki and found that the deletion didn’t seem to affect usage.
Will this kind of ID change affect other aspects?
You will lose the review history for those cards, and you’ll need to force a full sync after making the change.
thank you for your answer.