For context, this is a Thinkpad E14 gen five. With 8GB soldered and one DIMM slot Flex mode isn not bad, I suppose.
Ah, it worsens for Lenovo as you move down their product line. Some IdeaPads ship with Alder Lake or Raptor Lake CPUs and soldered single-channel DDR4-3200 RAM, with no ability to upgrade. I would be happy with just a single RAM slot for upgrades anything beats having to deal with soldered single-channel DDR4.
Silver linings, I suppose, or the opposite for the fully soldered 3200 models.
Single channel is also bad for the iGPU.
DDR5-5200 may actually perform worse than DDR4-3200. You have to consider the frequency and latency.
DDR4-3200 CL16 is about equal to DDR5-5600 CL36.
That is fascinating, I forgot how much CL increased with DDR5.
Igpu gains much more from bandwidth than delay.
Dual channels will make a larger difference.
So, does it make a substantial difference?
Not really, I suppose. But I believe that dual DIMM slots for real dual channel are not too much to ask for.
I have been out of the loop with modern laptop hardware, and when I found out my latest laptop had soldered RAM, I was a little disappointed, since I was looking forward to upgrading. 
Oh, I feel for you. but hope you managed to upgrade