[semi-extrinsic]

There have been instances of 1000 year (millennium) bonds, such as Danish energy company Orsted in 2017, Canadian Pacific Corporation in 1883(!), etc.

100 year (century) bonds are a bit more common - Disney issued a century bond in 1993, for instance. Argentina (!) issued a century bond in 2017, which it defaulted on last year, leaving creditors with around 55 cents on the dollar.

In general, long term (implicitly high risk) bonds become attractive in low yield environments such as we had been in for a couple of years up until the absolutely humongous amount of stimulus triggered by the current pandemic.