Have I understood this correctly?
Short answer, no.
Longer answer. The shareholder won't get any direct increase in personal taxes, but it means the company will have less cash to issue as dividends.
FY22 - Company makes £1M profit, it pays 19% Corporation Tax of £190k and has £810k to do with as it wishes (assuming profits = cashflow - this is a VERY simplified example). It chooses to pay 50% of it's profits as a divi and re-invest 50% - it pays £405k in divis to shareholders who pay tax at their relevant %age depending on tax code/ if it's in an ISA or SIPP etc.
FY23 - Company makes £1M profit, it pays 25% Corporation Tax of £250k and has £750k to do with as it wishes . It chooses to pay 50% of it's profits as a divi and re-invest 50% - it pays £375k in divis to shareholders who pay tax at their relevant %age depending on tax code/ if it's in an ISA or SIPP etc.
So while the shareholder hasn't paid the extra tax, their divis have gone down.
OR
FY23 - Company makes £1M profit, it pays 25% Corporation Tax of £250k and has £750k to do with as it wishes . It chooses to continue paying £405k of it's profits as a divi and re-invests the remaining £345k and shareholders get slightly lower growth in the future - shareholders pay tax at their relevant %age depending on tax code/ if it's in an ISA or SIPP etc.
So while the shareholder hasn't paid the extra tax, their growth prospects in the company have gone down.
OR
FY23 - Company makes £1M profit, it pays 25% Corporation Tax of £250k and has £750k to do with as it wishes . It chooses to re-invest £405k and shareholders get the 'normal' level of growth, but can now only pay £345k of it's profits as a divi - shareholders pay tax at their relevant %age depending on tax code/ if it's in an ISA or SIPP etc.
So while the shareholder hasn't paid the extra tax, their divis have gone down.
There could be another OR which is that the board all cut their salaries to ensure shareholders don't miss out, but this isn't the Laughing Lemons board.
Short summary - Shareholders will pay no extra personal tax, but will feel other negative effects most likely.
Optimistic summary - Shareholders will pay no extra personal tax, but the increased tax take for the government will have a positive societal effect and they will end up much happier by having good services and security.