At https://spaceweather.com on June 23rd 2021 astronomers announce the discovery of a comet so big it might actually be a small planet. The object has a handle – 2014 UN271. It was found during the Dark Energy Survey and as yet is well outside the inner solar system. It is estimated to be at least 100 km across [around 60 miles wide]. It is 2 or 3 times the size of Comet Hale Bopp in the 1990s. It won't be anywhere near our vicinity until 2031. Preparations for a mission are at the discussion stage.
At https://phys.org/news/2021-06-space-orbit-oort-cloud.html … which concentrates on the idea the orbit of this comet is elongated, and involves the Oort Cloud. They say it may be even bigger – anything up to 370 km wide. That is over 200 miles across. Happy days – and it won't come anywhere near the earth, they say [but will orbit around the Sun]. A lot depends on how it might brighten – and what effect the solar wind may have. Good test for the Thunderbolts electric comet idea. That has run on a flat per previous comets – but they are ever hopeful.