You can uncheck a pin topic for yourself by just clicking the pin icon. 
If you’re looking for a pinned thread, you personally unpinned try this:
https://boards.straightdope.com/search?q=in%3Apinned
Handy how to’s for the SDMB.
Steps to Mute a Tag or Category (Forum)
Click your user icon next to the menu.
Click the last Icon for Profile
Click Preferences
Click Tracking
The lower right hand box is for Muted Tags.
Enter tru and you’ll be prompted for trump. Click trump.
Click Save Changes
.
How to Reply as a linked Topic
Click Reply, in the upper left corner of the reply window is the reply type button, looks like a curving arrow point to the right.
Choose Reply as linked topic and it starts a new thread. As an example, you can choose GD, IMHO or The Pit for it.
That is actually the best method.
To determine or change Theme:
- Click on your Avatar next to the Menu. (Upper Right Corner)
- Select Profile (The last symbol on the right)
- Select Preferences again
(The gear symbol)
- Click on Interface. (Should be the second to last choice.)
To determine or change your Email preferences :
- Click on your Avatar next to the Menu. (Upper Right Corner)
- Select Profile (The last symbol on the right)
- Select Preferences again
(The gear symbol)
- Click on
Emails
- There are 4 dropdowns, set these as you wish.
Save Changes
So click the Search button 
In this search box, click the sliders button on the far right.
Click
Advanced filters
Include some search words, from your example I’m using solar Truck.
In Posted By, enter the name of the poster
Include a date range if possible to narrow it down. I selected Posted after & 01/01/2020
Below I read is a pull down box that says any, pull down and select I created or are the very first post
All this should narrow it down a lot. This gets no results as Truck apparently wasn’t in the thread, but I removed Truck and got only 4 hits including this thread of course.
What I used in the end:
solar @Sigene after:2020-01-01 in:first
@me is a shorthand in searches for @yourusername, a way to avoid using advance search.
- Click the Link button

- Paste the URL (link) into the “Link or Topic” field
- Type out a description in the Link Text field.
- Click Insert
Example: SDMB