The Gov.uk website has some useful information. I typed in the BMW Z4, which should have either the Plus Four B48 or the Plus Six B58 engine. What's interesting is that although the Z4 can have the Plus Four or Plus Six engine the Gov.uk recall info does not differentiate between the two. Perhaps the BMW dealers might do so once they investigate a specific case. Also we don't know which 'year' of engine was used by MMC, so although 2023 built Z4's are not affected, it's possible (though I suspect unlikely) that MMC's stock of engines for 2023 builds might include some BMW build year 2022 engines. Certainly concerning enough to ask some further questions.

2019 build

Replace the Starter Engine Motor - Reason for recall
For affected vehicles there is a concern involving water ingress and corrosion to the starter motor for where a short circuit cannot be ruled out. It is strongly recommended to park the vehicle outdoors and not in the immediate vicinity of buildings until the repair has been carried out.

2020 build

As above, in addition ...

Replace the Starter Engine Motor - Reason for recall
The Safety Recall relates to the engine starter motor. The fault relates to the RSW22 starter RWT (reinforced water tightness). It was found that with RWT starters an increased abrasion of the magnetic contact can cause the growth of deposits at the lowest point of the relay interior. This in turn may increase the relay contact resistance resulting in false starts or even causing short circuits and possibly a thermal reaction. In case of a short circuit the possibility of a thermal event cannot be excluded. This may happen while attempting to start the vehicle or while driving due to vibrations causing a short circuit due to moving deposits.

2021 build

As above, second issue only (RSW22 starter)

2022 build

As above, RSW22 starter

2023 build

No recalls

Plus Six "Rachel"
Volvo C40