In direct conversion transceivers, the LO leakage is pretty much a given. Some systems, mainly OFDM systems like Wifi, deal with that by simply leaving the DC carriers unused. And that's it. No further treatment is neeeded.
The same happens in 4G downlink, and I suspectsuspected¹ it stays the same in 5G, at least for the non-mmWave frequencies: The DC carrier remains unused, and no DC offset cancellation is necessary.
In the uplink, there's no DC problem, because by design, this whole OFDM system is shifted by half a carrier spacing, so that LO leakage ends up on a null of all subcarriers.
So, user equipment doesn't do much DC offset cancellation in the digital domain. If anything, there might be slow control loops that calibrate out possible ADC and receive chain offsets.
(now, being honest here: it's impossible to know what every user equipment there is does. There probably are user equipments that do some additional DC offset cancellation, as part of a digital predistortion / compensation scheme for a lot of the, especially nonlinear, imperfections of their RF chains. Will they be a single building block "leakage removal"? Probably not, as that, as described, is already done by OFDM principles by design.)
¹ but AlexTP points out that this is not the case for NR