It's more work then ready made fillers, but worth it in applications where strength matters. Mixing is annoying, if you put too much hardener in it becomes unworkable quickly. Best to put too little than too much IMO. And it's a PITA to sand after its dried as it's so hard, so try not to overfill.
Two part wood filler is the business. Like so:
https://www.toolstation.com/shop/Painting+%26+Decorating/d150/Fillers+%26+Putty/sd3169/Everbuild+High+Performance+Wood+Filler+500g/p55454
They come in different colours too.