It is not the force applied or the hardness of the toothbrush bristle that makes the brushing effective, but the technique.
You can use a manual toothbrush if you master the brushing gesture: it must be effective in removing plaque on all sides of all teeth. At the same time, the gesture must remain atraumatic, i.e. not aggressive to your gums.
Electric toothbrushes are a major asset in the removal of bacterial plaque, we encourage you to use them.
People with narrow gums that tend to recede are encouraged to use manual toothbrushes or non-rotating (often oval-headed) electric toothbrushes.
A plaque disclosing product can be used at the beginning of the learning process for training purposes: as soon as you have learned to detect bacterial plaque, it is no longer necessary to use it, except occasionally at the end of brushing to check if it has been effective.