If you sell your AM4 kit the outlay in cost wont be too much different to grabbing a 5700X3D tbh.
If the 5700X3D was still on the cheap side I'd have went for that all day long, but at £200 I find it steep unless you don't want to deal with a rebuild, which you'll essentially be doing anyway due to the new PSU. I'm saying this as someone that opted for a 5800X3D a couple of years back rather than jumping on AM5 too, but current AM4 pricing really isn't value for money anymore for many.
For reference, you can pick up the 7600 for around £170 at the moment, £80-90 for some decent RAM, £100-150 for an entry level to decent B850. Seems like a no brainer to me, hell I'd go the extra mile and consider a new case too so it feels like a whole new build!