Can I use a 61-W adapter of Macbook to charge my iPhone 12 Pro Max?

no, not unless the connector does not fit and you force it, or if the charger output higher than 5volts

rechargeable devices are never approved if they don't have an upper level of current they use when charging if they didn't they would be a fire hazard.

if your ios device was made to be used with the say 20watt charger then

watt == volt * current

volts are 5 and lets say it could fully use 4 amps to max out the 20watt and you connected it to a 61watt charger then it would still draw 4amps even if the charger were able to provide 12.2amps

Yes, just did so last night.