Windows server AD network migrating to RDP/Thinclient Downsides?

My background Linux server environment and networking now sitting as 'the only person with a clue' in a Windows 2019 AD network (on site archaic server with no offsite backup!) with a very ropey external IT company using Team viewer to manage our 20x Win10 desktops and no one has any idea what our aging hardware will do when presented with Win11 (80% failure is my guess)

New IT guy who I'd like to employ is saying ... This client solves Win11, RDP to a new cloud server, users all become local users on the server with their own file space. It dumps the £4k Sophos renewal for 20x desktops and we can go to Win Defender or just beef up security on the server.

Some users are on local Outlook and Excel/Word but for most all their work is on cloud based software via a Web browser with 365 or Gmail and Google cloud. (Yeh we haven't even got everyone on the same Cloud service!)

I'm trying to make sure I've not missed any think obvious for downsides here?

Anyone want to Admiral Ackbar and shout its a trap before we go for it?