Hello. Although the 5th gen iPad Pro 12.9 (2021) is a bit thicker, it is compatible with the Logitech Slim Folio Pro. I have just tried this out and it works perfectly.

Hello, as the 2021 is 0.5 mm thicker than the 2020, it can only just be inserted into the rubber socket. But you can get it in. Charge the keyboard until the LED above the battery symbol is permanently green. To pair, wait until the keyboard is listed in the iPad's Bluetooth list, then press and hold the Bluetooth button to the left of the battery symbol for up to 20 seconds. The pairing number appears on the keyboard (not on the iPad).

Hello. This Slim Folio Pro keyboard is compatible with the latest iPad Pro 12.9 (5th gen.). Just tried it out.

I have an older iPad and therefore cannot answer the question. I recommend checking the Logitech website.