How do I run my old project?

I need to run an old project with color picker and color variable plugins that are sdk 1 (I can no longer load the project with the latest versions of C3)

1. It says I need to run LTS version to be able to run the project.

2. Using the latest LTS version my project says it was saved with a more recent version (420?) so it cant be opened.

So Im stuck in an infinite loop?

What do I do?

Thanks

P.S When I say 'old' project I mean its about 1 year old.

P.P.S I have already had to basically give up updating my main project (which is available on the stores and has thousands of users) but I can no longer update it because of these sdk breaking changes.

...

2. Using the latest LTS version my project says it was saved with a more recent version (420?) so it cant be opened.

...

The latest stable version (r449-2) still allows opening SDK plugins version 1. Therefore, it is unclear why this is the case.

then open it in the version you need.(r420)

editor.construct.net/r420

Not sure you understood correctly. When I open with 420 I get the message:

This project cannot be opened since it was saved in a newer version of Construct. The project was saved in 420.2, and you are currently using r420...etc

Also, the message about the color plugins in the latest version of C3 reads:

Note: legacy (SDK v1) addons are no longer supported in this release of Construct and so cannot be installed. The last release that supports legacy addons is the r449 LTS release. See the LTS releases page, or contact the addon developer for an updated version of the addon.

Not sure you understood correctly. When I open with 420 I get the message:

This project cannot be opened since it was saved in a newer version of Construct. The project was saved in 420.2, and you are currently using r420...etc

Then open it in version (r420.2)

editor.construct.net/r420-2