Usually the information is pretty vague because the manufacturers hope people use installers rather than do it themselves, and probably the installers might information-hide.
At least from Ring doorbell usage (I can't comment on Eufy, but it might be fairly similar) the resistor was only needed on older doorbells.
On newer doorbells, it's not needed. Nevertheless, I went for the topology where it's powered through a solenoid (i.e. the solenoid inside mechanical door chimes), so there is a bit of resistance in effect. It sips power, just enough to keep it's internal battery topped up, and that small amount of power doesn't energise the solenoid. The Ring doorbell is designed to act like a short across its power terminals (well, close to a short; I imagine it current-limits) when the user presses the button, so that the mechanical chime can work too. Presumably the older doorbells couldn't do that, so they would have to have a resistor if there was no solenoid in series.
I can recommend these parts for a Ring doorbell (specifically the "Ring Video Doorbell 4") because it's been in use for 3 years, with no issue so far.
I used a Friedland E3539N transformer, rated at 12V, and you'll see about 22 V AC on the output with a multimeter, and wired the Ring doorbell, and a mechanical (i.e. solenoid) door chime (Honeywell "Ding Dong D117") both in series. That works great.
If your doorbell requires a similar voltage and has an internal battery, then there may be a good chance that the items mentioned will work for you.