Not quite that simple
Quote from HMRC -
You’ll need to register by 5 October in the second tax year after you started trading if you earned more than £1000 from self-employment in the previous tax yearSo,
for example, if you had Sales of more than £1000 in the year to say 5th April 2019, (that is trading started 6th April 2018) then you
MUST register as a sole trader (or a partnership if there are more than one of you running the business and/or taking drawings (wages/benefits) from it, by 5th October 2019, etc
The £1000 rule applies to every year, so as soon as you go over that at the end of any financial year, you must register with HMRC the following October
Then to make matters less complicated (according to HMRC

) HMRC’s ‘Making Tax Digital’ programme is being phased in over a number of years, following the announcement in 2015 that it was the Government’s intention to eventually abolish the Self Assessment tax return.
MTD will eventually cover all sole traders whether they are VAT registered or not as below:
April 2022: MTD will be
compulsory and extended to cover all UK VAT registered businesses from 1 April 2022
April 2023: MTD will apply to taxpayers who file Income Tax Self Assessments for business or property income of
more than £10,000 a year; but teh aim is to have all sole traders caught in the MTD system
You must use compatible software to keep records, Excel is not sufficient, and just submitting VAT returns online is not enough to be MTD compliant.