Not every screen in Sage is available in web screens. I hadn't noticed myself, but this appears to be one of them.

There is no mention of which version you are using but the COA screen is available 2021 (V6.8) web.

Where?  I have never seen the COA screen in web screens.  The report is there, but not the functional screen.  I consider this a major lack of functionality in web screens.

Exactly where it should be, General Ledger, G/L Accounts, Accounts :-)

That is not the Chart of Accounts screen; that is the Accounts screen.  The two are different.  The COA screen shows all accounts in one list with current balances, account type, and other info.

You are correct, I misread which screen was being inquired about.

Is it not possible to make your own screens for the web ?

Yes. Download and install the Sage web SDK and start coding.