Which changes are necessary for XM and XMTrading applications to both be approved and not rejected by Apple Guideline 4.3? There are two applications:
One you can see it directly in app store: https://apps.apple.com/gr/app/xm-trading-point/id1072084799
The second one I'll share it to you via Google Play: https://play.google.com/store/apps/details?id=com.xmtrading.webapp
When the two aforementioned apps are being submitted to the same countries then they might be rejected with reason:

Guideline 4.3 - Design
This app duplicates the content and functionality of other apps submitted by you or another developer to the App Store, which is considered a form of spam.

Which are the minimum amount of changes to be done in order for the two apps to not be considered similar and both be approved ?
Apple Developer Guideline 4.3 states:

4.3 Spam
Don’t create multiple Bundle IDs of the same app. If your app has different versions for specific locations, sports teams, universities, etc., consider submitting a single app and provide the variations using in-app purchase. Also avoid piling on to a category that is already saturated; the App Store has enough fart, burp, flashlight, fortune telling, dating, and Kama Sutra apps, etc. already. We will reject these apps unless they provide a unique, high-quality experience. Spamming the store may lead to your removal from the Developer Program.

This means you already have more than one app that does the exact same thing except there's slight variances.  This is not a new rule, it's been in place for years.  Apple started really enforcing it about 2 years ago.
Your options are to either talk directly to Apple about what, specifically, caused them to reject the app or you can do what they suggest and put them into a single app.
There's nothing in 4.3 that states what you have to change, that's going to be different for each app.  Apple only states you must &quot;provide a unique, high-quality experience&quot;.