iPad Air(4th Gen) or iPad Pro
Which iPad should I buy I am a architect and need for the same I am unable to decide
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I am not sure of the amount or availability of such apps on iPad/iPadOS.
CAD apps are sparse in the iOS App Store for iPads ( and not very intuitive ) and home interior rendering apps are almost non-existent, if they exist, at all.
I believe you should look elsewhere for the tools you need.
Microsoft Surface/Surface Pro tablets with full Windows OS support maybe a better match for the kinds of work you need to accomplish.
OR even a full Apple MacBook/MacBook Pro, if you want/wish to stick with purchasing something from Apple.
Many architectural applications available for macOS VS iPadOS. Many more.
iPads tend to lean more toward graphic/Web design and marketing, product/industrial/conceptual/sketch design ( you could do conceptual/sketch home designs on an iPad, but that would be about it! ), normal digital art/technical illustration art and design and digital painting.
iPads are not really geared toward normal engineering or architectural design/engineering disciplines.
You really need to look at and purchcase a Microsoft Surface/Surface Pro tablet for the type of things you really need to do or a full featured Apple MacBook/MacBook Pro.
Always purchase the right tools for the right job!
Sorry & Best of Luck to You!