Pokemon Home now allows someone with the Switch versions of Pokemon FireRed and LeafGreen to send creatures they caught to Pokemon Home. However, this is a one-way trip, as you can only deposit them. Everything works once someone performs the latest game and app updates.
How it works is once you update your game and app, you can take any Pokemon you caught in FireRed and LeafGreen on the Switch and deposit them in your Pokemon Home boxes. It will then no longer be in the original game. Those characters can then be sent into titles like Pokemon Scarlet, Violet, Legends Z-A, and Champions. However, that is described as a “visit” for Pokemon Champions.
There is a reward for finishing the PokeDex from these Switch games too by catching and registering them in-game. You can get a Celebi in Pokemon Home as a bonus once it recognizes you did so. Based on the screenshot shared in the announcement, it will arrive at level 50 with the Natural Cure Ability and Quirky Nature. The moveset should include Heal Bell, Leech Seed, Recover, and Safeguard.
Here’s that official screenshot of the Celebi.

Pokemon FireRed and LeafGreen Versions are on the Switch and playable on Switch 2, and Pokemon Home can be used on the Switch, Switch 2, and Android and iOS mobile devices.