Architecture dependency issue associated with malicious payloads

My question is regarding architectural restrictions associated with backdoor/bind/reverse tcp payloads used typically to gain shell through exploitation.

In a situation where whether the target box architecture(x86 or x64) is unknown.

Would an x64 payload work on a x86 architecture without user intervention?(windows prompting the user to run executable in a capability mode)

Is there a solution for payload delivery that does not have architectural dependencies?

Would encoding a x64 payload with an x86 encoder create compatibility issues when executed?

Any help is appreciated! I appreciate it because I'll save time asking here rather then manually testing.