What problem does this address?

Currently, when using the core/table block in the block editor, pressing the TAB key inside a table cell unexpectedly sends the focus all the way to the end of the page, rather than navigating to the next cell. Additionally, each cell requires a mouse click to activate before you can start typing in it.

What is your proposed solution?

It would greatly improve accessibility and usability if keyboard navigation within the table were enhanced.
Ideally :

• Pressing TAB should move focus horizontally from one cell to the next (left to right).
• At the end of a row, TAB should jump to the first cell of the next row.
• Shift+TAB should work in reverse to move focus to the previous cell.
• Arrow keys or Enter could optionally support vertical navigation.

This would make it much easier to input data into tables, by adding the ability to navigate using the keyboard, improving both efficiency and accessibility (in line with WCAG 2.1 standards).