Looking up technical specs for the drive it’s often mentioned on data sheets (often as conventional magnetic recording drive or else shingled if SMR). Other than that third parties have compiled lists and many but not all Amazon pages in tech specs mention it if you look closely. Try searching drive-model and cmr and then smr and see what comes up. Beware some drive families different sizes of drive may be cmr vs smr. WD red pro and ultra star DC line are all CMR, WD blues many are SMR. WD black as far as I know are all CMR. WD red (non-pro) can be SMR I believe.
I’ll be honest, the real difference is getting a 7200 vs 5400 RPM drive, particularly one with a larger cache, I’d always go for 7200 except for purely offline backup stuff.
In terms of external drives and shucking, it’s largely a crapshoot. You can try searching what drives others found in a model, however they’re subject to change.
Bottom line: If money is tight and it’s just you, you can absolutely do SMR and 5400 RPM external drives and have a smooth experience as long as we’re talking re-encodes not raw Blu-ray remuxes (I have seen an external 5400RPM SMR drive choke and fail trying to smoothly play a file at 24MB/s bitrate but it worked fine with 10MB/s re-encodes, even those with burst rates of 17MB/s). If you can afford a bit more try to go 7200 and CMR.