You can't do an in-kind trustee-to-trustee transfer. As you found, you would have to sell these investments within the Capital Group Roth IRA, then do the trustee-to-trustee transfer as a cash transfer.
Selling investments within a Roth IRA has no individual tax implications. However, selling investments in partnerships held by an IRA that generate Unrelated Business Taxable Income (UBTI) could result in the IRA owning Unrelated Business Income Tax (UBIT) that would reduce the value of your Roth IRA.
