Memory limit issue when trying to update add-on

I’m not sure if this is an EE issue or an issue with the Structure add-on. I have updated the files for Structure to 4.3.12 on EE 4.2.1. The CP gives me the option to actually perform the update - here’s a screenshot

When I click on the update button, at first I was getting a blank screen. So I set debug to 1 in admin.php and then got this error when trying to update Structure:

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 40381 bytes) in /path/to-my/system/ee/legacy/database/drivers/mysqli/mysqli_result.php on line 168

PHP info shows memory_limit at 128mb - screenshot.

I did notice that the server/site is on PHP 5.4.x though. I’m going to see if the client will upgrade that to something higher.

Besides, that, I’m not sure what could be causing the issue.