the problem with rpi4 would be the disk. You'd have to use and external USB disk, which is much, much slower and not as much stable. The time it takes to sync the bitcoincore could go from 1 to 2 weeks on an external SSD, and more than 1 month in an external HDD.

Also, in my experience, external drives randomly loose connection to the host (mostly HDDs, never had this happening with SSDs though). It happened to me about once a month or so. So you'd have to be checking your setup frequently for that.

If you have a stable USB SSD connected to your rpi4, i'd go for it.