URGENT _xlfn. appears since today creating #NAME error

Since today I suddenly have _xlfn. appearing for certain functions and I get the #name error. It seems to have to do with using new functions in older excel versions. I just use Office 2021 like I do since I bought it. 
Is there something wrong with an update or something??

All sheets with 'new' functions are suddenly useless. I tried updating, restarting excel, restarting PC but I can't find a solution yet.