Not speaking in any professional capacity, but HMRC has bigger fish to fry.
That said, under the old stricter rules, a lot of bike shops would offer me C2W over the limit or on sale bikes, then retract when they found out who my employer was. Shops seemed more worried than scheme users.
Our own scheme had a “50% of mileage must be commuting” but never checked to my knowledge.
So it’s down to Rule 1. If you know you aren’t going to use it for any commuting, and you can afford to buy the bike without using the scheme, it’s on your conscience whether you use the scheme to make a saving to avoid adding to the already overflowing tax pot that funds the public services you use.
If you think that puts me on a high horse, at least I’m further away from the manure!