32-bit app compatibility with macOS High Sierra 10.13.4 and later. what do i do now?

If you're going to upgrade past Mojave, check the Mac App Store or the developer's website for updates, or find a replacement.

If not, you can ignore those notices.

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32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support

You need do nothing immediately: but any 32-bit applications you have will cease to work with the next system, expected in the near future. (There may be the odd app which won't work properly with Mojave.)

It's up to developers of apps to produce 64-bit versions. Unfortunately there are a number of useful programs which show no sign of ever being updated. This leaves you with the uncomfortable choice of finding something else similar, or not upgrading beyond where you are now.

You should check which applications you have which are still 32-bit. Open Applications/Utilities/System Information: in the clumn at length, in the 'Software' section, click 'Applications'. It will take some seconds to open the list, which will list a lot of stuff you don't recognize, including all Applescripts (I don't know whether 32-bit scripts will work when Applescript is updated - assuming it isn't removed). There is a '64-bit' column to the right, flagging each application as 'Yes' or 'No'. You can click on the column header to group all the 'No's together. Look through and see whether there is anything essential.