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Try using below CSS:

<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>

Also, if it is not working using alternate CSS (As modern pages does not support this) then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

References:

1. Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions
2. Supported customizations for "modern" pages
3. Sharepoint 365 - Add Custom CSS to Modern Pages

Try using below CSS:

<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>

Also, if it is not working using alternate CSS (As modern pages does not support this) then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

References:

1. Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions
2. Supported customizations for "modern" pages
3. Sharepoint 365 - Add Custom CSS to Modern Pages

Update:

You can also try this:

1. Click on settings (gear icon) > Change the look > Header
2. Upload white transparent image as site logo and site thumbnail
3. Save

Check my answer given on this thread for more information: SharePoint Header Site remove

Try using below CSS:

<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>

Also, if it is not working using alternate CSS then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

Reference:

Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions

Try using below CSS:

<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>

Also, if it is not working using alternate CSS (As modern pages does not support this) then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

References:

1. Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions
2. Supported customizations for "modern" pages
3. Sharepoint 365 - Add Custom CSS to Modern Pages

Try using below CSS:

div[class^="logoCell-"] {
    display: none !important;
}

Also, if it is not working using alternate CSS then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

Reference:

Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions

Try using below CSS:

<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>

Also, if it is not working using alternate CSS then you can try adding it using SPFx Application customizer (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

Reference:

Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions