Many of newer offline installers from this year published without signed installers. Are code signing certificates too expensive or why the installers untrusted now?

Are you sure it's not an issue of the certificate being untrusted by your system, maybe certificates list not being updated?
Older certificates are from DigiCert, newer ones from Sectigo. Also, while until recently they were SHA1, the most recent seem to be SHA256.

Certificates schmertificates!

I never trust them! Not even if they have the correct intermediate certificate in place!

They're frankly useless in most cases. Especially if you use something like InnoExtract to rip em' open and dump the contents on the floor.

Attachment shows the differences between Windows 10 and Windows 11.
I don't know why the cert is missing in the Windows cert store to validate the signed installer.

Found a solution...a missing DigiCert certificate was the issue. After install the cert the installers now works correctly.