Hunting loaners is particularly enticing on Lyriqs in particular, but there aren’t that many to go around. Unless it changed recently, demo miles can affect the lease, although it doesn’t in many cases since these are often under 1k miles. See here. The mileage limit for lease eligibility is 7,500.
Also, slightly off-topic, but the limit for BMW loaners is 15k now, not 5k. Although 15k significantly affects the residual and raises other concerns like tires (I recommend taking off the garbage f-ing run-flats at inception and putting them back on when returning).