Star Alliance have a cross upgrade scheme. But has onerous t&c's and needs an expensive base fare.
https://www.staralliance.com/en/redeem
Star Alliance Upgrade Awards
Use your miles or points to upgrade your travel experience
With a Star Alliance Upgrade Award you can use accumulated miles or points to "pay for" an upgrade, allowing you to fly in a class of travel that is one higher than your original booking. This award is applicable across all 26 member airlines. Star Alliance is the only alliance to offer this benefit between all its airlines.
How to upgrade:- You must have a ticketed reservation in an upgradeable booking class to request a Star Alliance Upgrade Award with your frequent flyer programme. Check their website to find out how many miles are required to pay for the upgrade and which booking classes are upgradeable.
- Your reservation must show the flight number of the airline operating the flight.
- Star Alliance Upgrade Awards are not available on codeshare flights. Star Alliance Upgrade Awards are not guaranteed and may not be available on all flights. Please check the special terms and conditions on the website of your frequent flyer programme.
- Miles that you use will be deducted from your account.
- Requests must be made at least 24 hours prior to departure to allow for the partner carrier to respond to the upgrade request. Use the online form of your frequent flyer programme to request a Star Alliance Upgrade Award.
Some airline forums have dedicated threads
UA
How to upgrade with UA miles on Star Alliance carriers
AC
Star Alliance Upgrade Awards post-2020
This may be having an effect-->
Asiana to be acquired by Korean Air. What will happen to my mileage and status?