The main difference between them is the way you pay tax and yourself.
Operating as a limited company you have to pay Corporation Tax of 19% on any annual company profits. As company directors usually pay themselves both a salary and dividends, only the salary will be subject to Income Tax and National Insurance. Their yearly salary and dividends will still need to be declared in an annual tax return and they will still receive a standard Personal Allowance of £12,500 unless their total income and dividends are over £100,000.
Operating as a sole trader, you can keep all your profits after you’ve paid income tax on them. The rate of income tax you pay depends on your income. Currently, there is a Personal Allowance of £12,500 which you pay 0% on, the Basic rate £12,501 to £50,000 is 20% and the Higher rate £50,001 to £150,000 is 40%.