Give a source that says they aren’t
You are kind of right but not completely.
The figures released daily cover everyone who has died within 28 days of a positive test regardless of cause of death. This gives them a quick figure. It will include some who have died of other causes but it excludes some who died of Covid-19 without a positive test.
The ONS figures released weekly cover only people where the death certificate mentions Covid-19 as one of the causes. Doctors do not list Covid-19 as the cause unless it is genuinely a cause. If they give a false cause of death, they are committing a criminal offence.
For the week ending 13th November, the daily figures give a total of 2,849 deaths within 28 days of a positive test. For the same week, the ONS shows 2,838 deaths where Covid-19 is given as one of the causes.
I've used the most recent week for which ONS figures are available. In other weeks the two figures are close. Some weeks the ONS figure is higher than the deaths within 28 days figure, some weeks it is lower.
Overall, since the start of the pandemic, 55,838 people have died in the UK within 28 days of a positive test. In the same time period, 66,713 people have died in the UK with Covid-19 named on the death certificate as a cause of death.
So yes, the daily figures include deaths from other causes. But they are not a huge overestimate of the number of deaths caused by the disease. If anything, they are an underestimate.