I suggest get a 2020 iMac or possibly a 2019 iMac. Previous models had various issues. The 2020 is the ultimate refinement of the 27" iMac.
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Add your own RAM, preferably 32GB, it is cheap.
... we decided to go for the fully loaded 2020 iMac ...
... The RAM (memory) can always be upgraded separately later. ...
Recognizing that the 2020 does have one peculiar issue of its own, (as noted by wilberforce and others previously) in that the speed of the RAM can be adversely affected if you install dissimilar DIMMs. For contrast: my own 2019 iMac still has the original two 4GB DIMMs that it came with installed alongside two 16GB DIMMs that I purchased aftermarket, for a total of 40GB -- and I did exactly the same thing previously in a 2012 iMac; in both cases, the computers took full advantage of that RAM with no issues.
However, if you do that with a 2020 iMac, performance can apparently be degraded. The preferred approach when upgrading the 2020 is to remove the OEM RAM and install four identical DIMMs.
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