Select multiple tabs by pressing down Ctrl, or select a range by pressing down Shift. Then drag the selected tabs together to desired location, such as:

• another Edge window to move the tabs to another window
• empty space to split the tabs out into a separate window

References:

• https://answers.microsoft.com/en-us/microsoftedge/forum/msedge_search-msedge_win10/merge-tabs-on-microsoft-edge/b8947858-6bed-47ef-a315-d6000f20d622