Not an accountant, but I think this is false

If you intend to hold to maturity then you should accrue the bond coupons over time, that’s the modal case

If part of your bond portfolio is available for sale, then you should use mark-to-market accounting, which prices in the present value of future coupons and the discount rate as well.

IIRC this was one of the issues with the failure of SVB, they were forced to sell their bonds and realize a huge MtM loss

Agreed. Note that the question was directed to someone who “would encourage people doing their own accounts to think of it like this”.