Retired cabin crew here. If someone particularly frail or with mobility issues needs help with putting cabin baggage in the lockers, majority of crew will help them stow it - not take the whole bag themselves, but assist with placing it. If a bag is more than about 8-10kgs, it would usually be tagged up, taken off and put in the hold. If the holds are already closed up, then it will follow on the next flight. Airlines now include as part of their general training, specific training on how to lift bags safely but if, when testing the bag for weight, it feels too heavy for the cc member to lift, or help lift, it’ll be put in the hold. If this happens to you, remember to obtain the “limited release” tag from the cabin crew as it has the matching bar code on it (in case it doesn’t make that flight and ends up in Timbuktu….)