I've been debating between getting the base M4 Mini and assembling a desktop myself with the Ryzen 9600X. Price-wise, both are around the same. Points in favour of the former:

1. Smaller form factor

2. Don't have to bother assembling anything myself

Points in favour of the latter:

1. I can install my favourite flavour of Linux (and Windows too, though I hardly use it any more.)

2. Easy upgradability, especially of memory and storage - I don't foresee upgrading anything else for the next 4-5 years. 16GB/256GB seems to be something I'd quickly outgrow, and the next bump up in configuration is a huge bump up in price.