The issue for the phone is that it cannot communicate with the sensor called "mic1". That particular sensor is located on the charging port flex cable assembly, so there are electrical signals that start out on the motherboard and travel down that flex cable to the sensor itself.
So when they say it could be a motherboard issue, that's technically correct since part of the signal travels through the motherboard. However, it's actually very rare that the problem is in the motherboard itself; in every case I've seen, it's been either the sensor itself or the charging port assembly has been damaged in some way. Either way, the fix is the same, to replace the lightning port flex assembly.
So yes, it would be well worth your while to replace that part rather than replacing the whole phone. The chances are very good that a new lightning port assembly will fix it right up just like new. You are, of course, free to take it to a repair shop if you want, but iFixit is here with guidance and the parts and tools you need if you want to tackle it yourself.
The SE 2020 is based on the iPhone 8 and shares several components, and one of those is the charging port assembly. So if yours comes in and says it's for an iPhone 8, don't panic; it will work just fine in the SE 2020. Here's the part that iFixit sells; if you're new to repair I'd suggest the Fix Kit version as it comes with all the tools and parts you need to do the job.
iPhone 8 Lightning Connector Assembly
Looking it over, unfortunately it appears the Fix Kit versions are currently out of stock, but you can certainly buy the parts individually as needed. Here's the guide giving you step by step directions on how to replace the lighting port assembly.
iPhone SE 2020 Lightning Connector Assembly Replacement - iFixit Repair Guide
I'd say read through the instructions, then you can decide for yourself if this is something you want to tackle. It is somewhat of an involved repair so if it looks like it's out of your comfort zone, by all means locate a repair facility who will do the job.
Finally, to address the last part of your question, no, this particular problem isn't unique to the SE 2020; there are several other models with that same sensor that have failed in the same way, so there's no advantage in changing to a different phone to get away from it. Since it's a microphone sensor, my guess is the failure is due to the seal getting old and allowing either liquid or contaminants in to cause the sensor to fail, which can happen with any phone, really.
So take a look and figure out if you're up to the job. If you get into it and need advice, there are a lot of very smart people on here who are happy to help. I'd be interested in knowing what you decide and how it all turns out, so let us know what happens!
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