There are two places in Safari where content blockers are managed. These are buried pretty deeply, so here's how to get there.
Under Settings - Safari - "General", make sure the "allow these content blockers" is set to "on". Please make sure Scroll is set to "on".
Next, under Settings - Safari (keep scrolling!) then you'll see "settings for websites". (This setting won't even be visible until you've got the main Content Blockers toggled to "on".)
If you have disabled content blockers for specific sites, you will see them listed here. If you have disabled content blockers for any Scroll partner sites, you must toggle content blockers back on for that site in order for Scroll to work.
Please note: in the content blockers section, if you have the setting “use content blockers on all websites” turned off, Scroll won’t work in Safari.