More recently I don't think any of the GMs are actually using supercomputers. Powerful computers, yes - but not anything close to supercomputers.
The only two instances I've seen an actual 'supercomputer' mentioned in recent Chess news has been:
* Ian Nepomniachtchi using Zhores (which is questionable given that the institute which runs it [Skolkovo] has Arkady Dvorkovich [chairman of FIDE] as it's chairman). I remember researchers questioning if Zhores was even suitable for the type of calculations which engines care about, so this looks like some PR move more than anything.
* There was a rumour a few years ago that Magnus Carlsen had some secret/private access to a Norwegian supercomputer. No real confirmation of this rumour occurred.
Both AlphaZero and Leela Zero (by their design and very optimal evaluation functions) also require much less evaluation - so they can naturally evaluate further.
The only two instances I've seen an actual 'supercomputer' mentioned in recent Chess news has been: * Ian Nepomniachtchi using Zhores (which is questionable given that the institute which runs it [Skolkovo] has Arkady Dvorkovich [chairman of FIDE] as it's chairman). I remember researchers questioning if Zhores was even suitable for the type of calculations which engines care about, so this looks like some PR move more than anything. * There was a rumour a few years ago that Magnus Carlsen had some secret/private access to a Norwegian supercomputer. No real confirmation of this rumour occurred.
Both AlphaZero and Leela Zero (by their design and very optimal evaluation functions) also require much less evaluation - so they can naturally evaluate further.