Haven't seen this elsewhere and it doesn't seem to be on your issues page.
I'm on MacOS v. 12.1 (21C52) using Chrome v. 100.0.4896.127 (Official Build) (x86_64) and Safari v. 15.2 (17612.3.6.1.6). And also on iPadOS 15.4.1 using most up to date version of Safari.
I'm getting odd/annoying behaviour when typing in the message box that I don't get on other forums and that I didn't get on Mumsnet before the update.
If I paste something in it stays highlighted so if I paste and type straightaway I delete whatever was highlighted.
Also, arrow keys seem to move the cursor oddly occasionally. I have tried to highlight a block of text and been unable to get the cursor to go up into the next paragraph when using the arrow keys, instead it's hopped down a line. This has only happened on Chrome so far and while it's happened more than once it doesn't always happen. I'm unclear what triggers it.
Also, if I accidentally click the back page button (or go back a page using Chrome's swipe feature) when typing a message and then swipe/click forward page my message used to still be in the message box, but now it's gone and I have to retype. 