Yes, I've gone in with Notepad++ and tweaked those settings to no avail, it does not matter whether they are true or false, or if their value is the default value or otherwise: the enemy HP bar, awareness level, and enemy level do not show up, so I guess I will just disable BetterUI for the time being, and just use the other mods.
Looking in the Forum at NexusMods it seems I am not the only one with this problem, so it might actually be a bug!

Found a comment on the website saying that there was an upload of BetterUI called BetterUI Reforged in a different website. I have downloaded it and it now seems to work showing enemy levels, health bars and awareness

disable all mods and start one after the other after a test login. and u know which mod do the problem. when u know which mod do the problem u can watch in the settings where u can check some options to solve the problem. i know from other games that some mods crash other mods so they are not compatible with them. sry for my bad english. i think its betterUI where u disabled a HP bar.

Yes, it's definitely BetterUI, which is a pity because the rest of the stuff that it does is quite useful, but I suppose I will have to disable it fully, because I have been turning different options on and off, and I am still not getting the enemy health bar and level showing.
If anyone has used the combination of the above mods without any problems, can you let me know how you have set them up?

The page for the UI mod mentions that it includes these settings related to enemies:

Show enemy level: Text, Stars, Both
Show enemy HP amount (includes bosses)
Aware / Angry status colored on enemy name
Custom render distance

I have not installed the mod myself or used Valheims mod loader, but I imagine that there is an opportunity to select/deselect these options when performing a completely fresh install of the mod.
And the page for the mod also says that when you do a manual install it will automatically generate a config file anyway at BepinEx/Config, which I expect gets placed in the games install directory. That looks like it could be an alternative way of manually changing the mod settings via notepad or another text processing app.

I would have also said to make sure that your load order is in check but I don't reckon that would be the problem with those other mods disabled. Generally if you don't want parts of one mod to be overwritten by overlapping contents of another mod, you put it later in the load order.