If Charles III doesn’t end up like Charles I, he should consider it a good reign.
“... If you can keep it!”
Britain has effectively been a ‘Royal Republic’ since 1760 when George III surrendered the revenues of the Crown Estate to Parliament in return for an annual stipend decided upon by Parliament.
That was the final nail in the coffin of Royal power, arguably it had already passed to Parliament in 1689 after the Glorious Revolution and the passing of the Bill of Rights, which bound the Monarch to Parliament.
The Crown has been a mere symbol for a very long time and subject to a quasi-republican Parliament.