If you use a high resolution but small display, the new update may come as welcome to you since you'll likely have a more usable interface. Before this update, people with small high resolution displays (such as a 14 inch 1440p laptop display) really had no other option but to deal with a tiny interface.

TF2 does not respect your operating system's scaling configuration, and even worse is that TF2 was designed at a time where average monitor resolutions (especially on mobile computers) were much lower. The new HiDPI support that has been added to TF2 a really good addition especially in the age of increasingly high resolution laptop displays.

For anyone using a relatively standard monitor resolution and size (such as 2560x1440 at 27 inches) this new update might seem like a downgrade to you as some UI elements might be too large. For example, in this screenshot:
As you can see, some elements are very large especially when you consider that this is a 27 inch 1440p display.

This will only help with VGUI based items. Some other parts people have been having issues with (such as the scoreboard) are not affected. Still, VGUI based items is most of what you come across and will be the biggest pain point for most users.

There are also some other regressions that haven't been mentioned, but will likely be fixed in a future update.

Step #1: Right click on the game and go to "properties"
Step #2: Under the "Installed Files" section, click the "Browse" button
Step #3: Now you should be in the root TF2 install folder, let's navigate to your TF2 configuration folder
Step #4: Open autoexec.cfg with your text editor of choice. If you do not see an autoexec.cfg file, create it.
Step #5: You are going to want to add the following to your autoexec.cfg
Step #6: Save the file and launch TF2
You're done, you should now have a more usable TF2 interface.

If you are still having issues, send me an email at catgirlapril@protonmail.com (gpg: https://april.nekoweb.org/email_and_gnupg.html) and I will try my best to help you solve whatever issue you may be encountering.