How to create a uniform look/identical nav menu header on multi theme site

I am using WordPress 6.5.4 and I am using Multi Themes plugin.

I have certain pages on my site that have different menu headers. This is because I have two plugins that each have their own theme, so I use the Multi Theme plugin to apply a specific theme for a specific page.

Unfortunately this means the navigation menu header is different on the respective pages of each plugin. The actual content doesn’t matter so much as the header, the main menu header looks very different on the different pages and one theme even doesn’t display the menu I created.

I would like to at least have the menu exactly the same on every single page. I’ve tried a header creator plugin, forgot the name, but it didn’t work, whatever header I created, was applied to only one theme (not sure if it’s a coincidence or not, but it was applied to the officially active theme).

Would appreciate any ideas.

Thank you.