Yes, can you safely use the 61W USB-C adapter to charge the MBP 14. I routinely use a 30W MacBook Air charger when I am outside. (I also tried the 20W iPad Pro charger for chuckles, and it actually works!) When I am at my desk, the Mac is powered by the CalDigit Element hub at 60W.
The Mac will draw as much power as it needs, and the charger will supply as much power as it can (up to the maximum rating). If the charger cannot supply enough power, then the battery will slowly drain (which happens to my 16" i9 under max load, but yet to see under the M1 Max).
According to various sources (Anandtech, NotebookCheck), the CPU uses around 30W at full load. The GPU can draw quite a bit more under full load.