Unfortunately, this is a very big limitation of Airtable. I would highly recommend sending an email to firstname.lastname@example.org and ask them to please support this functionality. This would be very useful for many of my Airtable consulting clients.
Airtable is a “platform of limitations”, and we have to come up with all sorts of workarounds on a regular basis. Probably the best thing you can do here is to create an automation, but I don’t think that Airtable currently gives us any way to do this with the built-in automation actions (which are also extremely limited).
In essence, the automation that you would want to create would look something like this:
When you’re done editing your rich text field in the original table, you would check a checkbox which then triggers an automation to copy & paste the RTF value from the original table into a RTF field in your other table. This is definitely not ideal & comes with its own set of problems (for example, what if somebody edits the RTF value in the new table?), but it could be a feasible solution.
I’m also not 100% sure that this will work, but I’m pretty sure that it will. I’m pretty sure that you can copy & paste from one RTF field into another RTF field, and it should retain the rich text formatting.
Maybe somebody else will come up with some better ideas.
p.s. I am a professional Airtable consultant and a Registered Integromat Partner, and the Integromat link above contains my personal referral code.