Open the OneLake menu bar icon and choose Add Account…. Your browser opens at Microsoft sign-in. After you authenticate, pick a short alias for the account (for example work, client-a).
That alias becomes the Finder entry OneLake — <alias> (on disk: ~/Library/CloudStorage/OneLake-<alias>/). Pick something memorable.
Choose Add Account… again from the menu. You can add accounts from different tenants. Each gets its own alias and its own folder in Finder.
Every signed-in account appears in the menu bar with its own submenu. The default account is marked with a check; switch the default from an account's submenu with Set as Default. There is no "active" account to switch between — each one is mounted in Finder side by side.
Open the account's submenu in the menu bar and choose Sign Out…. Your data in OneLake is untouched.
After a long idle period your tenant may require re-authentication. The menu bar header shows a warning when that happens. Sign the account out and add it again to refresh the token.