How do I migrate my Keychain's "Local Items" to a new Mac?

I just managed to get my keys to my new mac (this only works if you still have access to the old Mac and can boot it up):

(on the old mac) Remove your current user's password
Create a new keychain (without a password)
Copy all keys in "Local Items" to your new keychain
Copy the keychain to the new mac
(on the new mac) Remove your current user's password
Add the new keychain file
Copy all keys in the new keychain to "Local Items"
Delete the new keychain
Don't forget to set a password again after that

It's a bit annoying as you have to click "Allow" for EACH item in the keychain but well, it's the only thing I found that works.

Assuming the old Mac works (or at least can start in Target Disk Mode and then be connected to another Mac and started up from using Option-Boot), turning on iCloud Keychain should sync all the items in the "Local Items" keychain to your iCloud account, and then enabling it on the new Mac would merge all the items between your iCloud account and the new Mac's "Local Items".

Here are some specific steps:

Sign in to iCloud with the old mac
Sign in to iCloud with the new mac (using the same AppleId as step 1)
Enable "Keychain" to be synced to iCloud on the old mac. This will cause every item in the "local items" keychain to get uploaded to Apple's iCloud. It will also make the "local items" keychain disappear on the old mac and instead an "iCloud" keychain will appear in its place.
Enable "Keychain" to be synced to iCloud on the new mac. This will make the "local items" keychain disappear on the new mac and instead an "iCloud" keychain will appear in its place. Every item from the keychain stored in iCloud to get downloaded into the iCloud keychain on the new mac.
Disable iCloud syncing of "Keychain" on the old mac and if prompted, opt to keep a copy of the keychain on the mac. This will make the "iCloud" keychain disappear but "local items" will appear again.
Disable iCloud syncing of "Keychain" on the new mac and if prompted, opt to keep a copy of the keychain on the mac. This will make the "iCloud" keychain disappear but "local items" will appear again.