I want to use an ssd to use raspberry pi with home assistant and I’ve found some information that an external ssd may require too much power and be unstable with the RP4. Is this true? Is one type of ssd better than another?
If you are using a SATA drive you need some kind of enclosure with USB adapter, since the Pi does not have a SATA port. This is a bit silly unless there is some reason you need to use some specific make/model that is SATA based; it can't be any faster than a USB drive since it is still using the USB port. The same goes for NVME drives.
Lots of small portable USB SSDs will work with the Pi without external power. Before you buy, try and find out what the power consumption is. You also have the option of using a powered USB hub, then it won't matter and any USB drive should work. This may be a bit awkward, but it is less goofy than the SATA enclosure (which would also require external power).
Generally if you search, eg., "samsung t7 power consumption" you will find a review somewhere giving some power consumption numbers. Sometimes these are just the manufacturer's spec, sometimes they are from actual independent tests. The figure is often in watts, which to convert to mA is:
Watts * 1000 / Voltage
The aforementioned T7 is spec'd to not consume more than 7.5 W, which @5V is 1500 mA. Considering that the most you can supply the Pi4 with is 3000 mA and that it seems to test at ~6.5 W (@5V, 1300 mA) peak, there is a good chance that this will work, but since this might be a bit idealized, not a guarantee. That said, you probably won't find a drive that takes much less (as generally they are going to be designed to use the USB 3.0/1/2 max).
If worst comes to worst and you need a powered USB hub, these are inexpensive and very commonplace.