Dandelion works by setting a flag in the transaction message. If the flag is set, nodes should perform the dandelion steps (ie, decide whether to continue dandelion routing or send to all peers), otherwise not. The existing transaction message format is unchanged.
An old node will not know of that flag, so will understand that message as it used to, and will ...
Never used Cake wallet, don't know if you can set custom nodes there.
If you take monerujo wallet & set an .onion remote node address then your wallet can only connect via Tor (Orbot).
If you want transact safely take your own full node: