If your if your toilet has always worked fine but now barely flushes, the most common cause is a clog.
First option is to try plunging the toilet. If you don’t see a significant change after plunging, it may need to be snaked, which requires the expertise of a professional plumber.
There could be a problem in the pipes.
However, if your toilet is a low-volume type, several years old, you may want to look into today’s low-pressure toilets.
The low-pressure toilets on the market today have been redesigned and function much better and more efficiently.
An experienced professional plumber is your best source to either fix the current problem or guide you in a purchase of a new low-pressure model.