Can I remove myself as a site collection administrator on multiple site collections?

Yes, you can remove your account as a site collection admin with the steps below:

1. Select All reports from the menu.
2. Click Create custom report.
3. Select Site collection or OneDrive for Business as your Object type (depending on your scenario).
4. Click Continue without saving.
5. Specify your target(s).
6. Click Next.
7. Click Run now.
8. Select all results using the top-left checkbox.
9. Click Remove permissions in the Quick actions menu.
10. In the Select users or groups field, input yourself or any other applicable user from whom you are removing administrative rights.
11. Use the Remove permissions drop-down to select Remove from site collection administrators.
12. Click Apply.

Note: If you use a custom report, turn off the auto-assign feature first. If you don't turn off the feature, the app will add your account whenever you run operations on your sites or when it crawls your environment.