XenForo v2.1.8 Patch 2 Centos 7 # php -v PHP 7.3.16 (cli) (built: Apr 10 2020 03:44:33) ( NTS ) Copyright (c) 1997-2018 The PHP Group Zend Engine v3.3.16, Copyright (c) 1998-2018 Zend Technologies with Zend OPcache v7.3.16, Copyright (c) 1999-2018, by Zend Technologies
I found the cause of the problem.
If I set the value to 558 or smaller, then the svg attachment works. 559 or above doesn't work.
However, further lower the value will crop the image:
Insert Thumbnail will be cropped like this: