You can access your Gnosis App account from multiple devices as long as you have access to your passkey.
We recommend to use a password manager that synchronizes your data across devices. Hence, you will be able to use Gnosis App from any device where your password manager account is accessible as it will save your passkey.
Also, you can add any Externally Owned Account (EOA) as an owner of your Gnosis App wallet in the Wallet Owner section in Settings.
This Externally Owned Account can be used to Import Gnosis App on a new device where a new passkey will be created by using the Import Wallet flow.