otpclient: /usr/share/glib-2.0/schemas/gschemas.compiled è già presente nel filesystem
otpclient: /usr/share/icons/hicolor/icon-theme.cache è già presente nel filesystem

@mreugene thanks, worked fine

The dependencies should be updated to have gtk4 and libadwaita. PKGBUILD should be appended in line 12 with:

 'gtk4>=4.10.0' 'libadwaita-1>=1.5.0' 

You can check what packages use the files with commands:

pacman -Qo /usr/share/glib-2.0/schemas/gschemas.compiled
pacman -Qo /usr/share/icons/hicolor/icon-theme.cache

In my case there were none. So I installed otpclient succesfully with overwriting these files:

yay -Su otpclient --overwrite /usr/share/glib-2.0/schemas/gschemas.compiled --overwrite /usr/share/icons/hicolor/icon-theme.cach

Please add libadwaita to the dependencies. otherwise it fails with:

CMake Error at /usr/share/cmake/Modules/FindPkgConfig.cmake:1093 (message):
  The following required packages were not found:

   - libadwaita-1>=1.5.0

Call Stack (most recent call first):
  /usr/share/cmake/Modules/FindPkgConfig.cmake:1166 (_pkg_check_modules_internal)
  CMakeLists.txt:96 (pkg_check_modules)

And after i installed libadwaita, I get the following error:

Packages (1) otpclient-5.0.3-1

Total Installed Size:  0,55 MiB
Net Upgrade Size:      0,01 MiB

:: Proceed with installation? [Y/n] 
(1/1) checking keys in keyring                                                                                      [#####################################################################] 100%
(1/1) checking package integrity                                                                                    [#####################################################################] 100%
(1/1) loading package files                                                                                         [#####################################################################] 100%
(1/1) checking for file conflicts                                                                                   [#####################################################################] 100%
error: failed to commit transaction (conflicting files)
otpclient: /usr/share/glib-2.0/schemas/gschemas.compiled exists in filesystem
otpclient: /usr/share/icons/hicolor/icon-theme.cache exists in filesystem
Errors occurred, no packages were upgraded.
 -> error installing: [/home/user/.cache/yay/otpclient/otpclient-5.0.3-1-x86_64.pkg.tar.zst] - exit status 1

@polslinux 5.0.2 fails to install, with

error: failed to commit transaction (conflicting files)
otpclient: /usr/share/glib-2.0/schemas/gschemas.compiled exists in filesystem
otpclient: /usr/share/icons/hicolor/icon-theme.cache exists in filesystem

Again it was forgotten to adjust the sha256sum :)