How to let non-sysadmins access design mode?
SYSAdmin is the user who has the privilege to access the entire database, including create sheets, change sheets design and rearrange tabs and sheets order. If you would like to let non-sysadmins change certain sheets' designs. For instance, grant sales manager the right to create sheets and change sheets design under "Sales" tab.
You may navigate to Hamburger Menu > User Acesss > Groups, and assign users as Group Administrator. In the next step, add a tab as Group Tab, enter the tab's URL slug in the Group Tabs field (e.g. /forms1, as it appears in the last part of the tab’s URL). Group administrators will able to add sheets to a Group Tab or make design changes to the sheets under a Group Tab.