It's possible but neurodegeneration isn't a laughing matter. Perhaps you should spend some time with the elderly.
Can there ever be a 100 ELO rated GM? And if so, do you think it will happen?

I know neurodegeneration is not funny, but I meant it in a way that a GM drops their rating on purpose.

Well they would stop being invited to tournaments and likely be incapable of entering either due to organiser suspision of game fixing as it is clear they are intentionally losing once no draw or win is achieved in so many games. Or that they dont meet the Elo level to enter. To the point that they would have to enter really low level tournaments that are opens and then lose those. I don't see them being allowed to enter after a point as it is clear they were sandbagging when suddenly they start winning again and playing much better. Hower there is an old GM who has a 1300 or so rating, I think it is decline in capability due to health not deliberate.
100 is a bit low, but there are many elder grandmasters who decline in playing strength.
They get invited to norm tournaments, to help youngsters achieving GM norms.
Then they play in open tournaments.

Earn a 2500 FIDE rating. In addition to the three norm requirements mentioned above, a chess player still must cross the 2500 rating requirement to be awarded the title of grandmaster. Vishwanathan Anand with Nihaal Sarin and Prangganandha, both are under 15 and have achieved already the grandmaster title.
Can there ever be a 100 ELO rated GM? And if so, do you think it will happen? Because I think it would be pretty funny if a GM dropped their rating.