Yet this is still safe as you need your unlock code to remove an account, even if the phone is already unlocked
The word “unlocked” in the context of phones usually implies the lack of a carrier lock on the device as originally manufactured and sold. It is not precisely correct to refer to phones originally locked to a carrier as unlocked when offering them for sale without disclosing any original carrier lock, as there are differences in supported frequency bands depending on the jurisdiction the phone was sold in that may make it incompatible with some carriers, whereas “factory unlocked” phones of the same model are usually world band phones and support all common carrier frequencies.
To recap: it’s fine to refer to phones which have had an unlock code applied to them as unlocked. To differentiate phones which came unlocked when originally manufactured, this second group of phones is referred to as “factory unlocked.”
Sorry to be pendantic, and this isn’t directed at OP. Most of this is inside baseball and is only important when buying or selling phones secondhand, in order to make sure the new owner is able to use their phone on a different carrier than the prior owner.
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All of the above is separate to anti-theft locks which are supported by Android and iOS devices, which must be removed before sale in order for the new owner to associate the device with their own personal Google or Apple account, respectively.
The Android and Google locks are independent of the above types of locks, and are account bound like the above locks, but instead of being linked to your phone service account, they are linked to your Google or Apple accounts. You could have one and not the other, or neither, or both. However, no end user benefits from a carrier or SIM locked phone. Mobile device OS-level blocks are important for security, however, and are under the control of the legitimate user and may be turned off anytime. To disable the SIM or carrier locks, you need the unlock code you originally mentioned.