BBC Reporting Scotland’s viewing figures according to their wikipedia page, averaged (past tense) between 500 000 and 600 000 with occasional peaks of 1 million for events such as the Lockerbie Disaster in 1988.
By 2019, Reporting Scotland’s average audience had fallen to 380 000, just below that of STV News at 390 000.
BBC Scotland’s news service and its audience is a closely guarded secret. Unlike other publicly funded bodies such as health boards or local authorities, the BBC, like the MoD or the security services, is exempt from the Freedom of Information legislation and need not reveal anything it does not want to.
However, if the decline from the late 80s at 500 to 600 000 to 280 000 in 2019, halving the audience is maintained in seems certain they are at around 300 000 viewers out of an adult population of around 4.5 million, 6.6%.