The 13" MacBook Pro (M1, 2020) still ships with the 61W power adaptor. The newer models (other than the Air) have slightly larger batteries and ship with the newer / larger power adaptors as well (67W, 96W). It's possible that Apple made some internal / circuitry improvements in the newer power adaptors when they were developing them to go with the new laptops. And with the new laptops now released there would be no reason to continue to offer the 61W power adaptor (although you might be able to purchase one from Apple if you contacted them, as a 'replacement part' that is probably still available even if not listed on their website. But why get that one if you can get one of the newer ones?)
With all that said, if you want to purchase a new / additional power adaptor for your MacBook then get one of the new and greater capacity ones. Either 67W or 96W will work fine with your MacBook. Even the 140W would be fine. The MacBook will only charge at the rate that the battery is suited for (the bigger ones may be more than what you need now, but who knows what you might have in the future?)
If you want to be absolutely sure, check on one of the following pages under 'Compatibility':
The 70W USB-C Power Adapter offers fast, efficient charging for your compatible MacBook Air or MacBook Pro. Buy now.
www.apple.com
The 96W USB-C Power Adapter offers fast, efficient charging at home, in the office, or on the go. While this power adapter is compatible with any USB-C–enabled device, Apple recommends pairing it with your 16-inch MacBook Pro for optimal charging performance.
www.apple.com
The 140W USB-C Power Adapter offers fast, efficient charging at home, in the office, or on the go for your 16-inch MacBook Pro (M1, 2021). Buy now.
www.apple.com