Install Transmission with Web GUI?

It doesn’t look like any of the documentation from OpenWRT’ Wiki page here works.

transmission-daemon, transmission-web none of which are found in the repos…

3.200 firmware version on the XE300.

did you run this command?
opkg update

screenshot of the execution show

Yes, only transmission-luci is available, no deamon, web etc.

root@GL-XE300:~# opkg update
Downloading https://fw.gl-inet.com/releases/kmod-3.4/ath79/nand/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_kmod
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/base/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_base
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/freifunk/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_freifunk
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/gli_pub/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_gli_pub
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/packages/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_packages
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/luci/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_luci
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/routing/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_routing
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/telephony/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_telephony
Downloading https://fw.gl-inet.com/releases/packages-3.x/ath79/glinet/Packages.gz
Updated list of available packages in /var/opkg-lists/glinet_glinet
root@GL-XE300:~# opkg find *transmission*
asterisk16-app-image - 16.10.0-1 - Image transmission application.
luci-app-transmission - git-20.341.57626-51f55b5-1 - LuCI Support for Transmission
luci-i18n-transmission-ar - git-20.319.48768-24a240d - Translation for luci-app-transmission - العربية (Arabic)
luci-i18n-transmission-bg - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - български (Bulgarian)
luci-i18n-transmission-bn - git-20.319.48768-24a240d - Translation for luci-app-transmission - বাংলা (Bengali)
luci-i18n-transmission-ca - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Català (Catalan)
luci-i18n-transmission-cs - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Čeština (Czech)
luci-i18n-transmission-de - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Deutsch (German)
luci-i18n-transmission-el - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Ελληνικά (Greek)
luci-i18n-transmission-en - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - English
luci-i18n-transmission-es - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Español (Spanish)
luci-i18n-transmission-fi - git-20.319.48768-24a240d - Translation for luci-app-transmission - Suomi (Finnish)
luci-i18n-transmission-fr - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Français (French)
luci-i18n-transmission-he - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - עִבְרִית (Hebrew)
luci-i18n-transmission-hi - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - हिंदी (Hindi)
luci-i18n-transmission-hu - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Magyar (Hungarian)
luci-i18n-transmission-it - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Italiano (Italian)
luci-i18n-transmission-ja - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - 日本語 (Japanese)
luci-i18n-transmission-ko - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - 한국어 (Korean)
luci-i18n-transmission-mr - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - मराठी (Marathi)
luci-i18n-transmission-ms - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Bahasa Melayu (Malay)
luci-i18n-transmission-no - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Norsk (Norwegian)
luci-i18n-transmission-pl - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Polski (Polish)
luci-i18n-transmission-pt - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Português (Portuguese)
luci-i18n-transmission-pt-br - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Português do Brasil (Brazialian Portuguese)
luci-i18n-transmission-ro - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Română (Romanian)
luci-i18n-transmission-ru - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Русский (Russian)
luci-i18n-transmission-sk - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Slovenčina (Slovak)
luci-i18n-transmission-sv - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Svenska (Swedish)
luci-i18n-transmission-tr - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Türkçe (Turkish)
luci-i18n-transmission-uk - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Українська (Ukrainian)
luci-i18n-transmission-vi - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - Tiếng Việt (Vietnamese)
luci-i18n-transmission-zh-cn - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - 中文 (Chinese)
luci-i18n-transmission-zh-tw - git-20.341.57626-51f55b5-1 - Translation for luci-app-transmission - 臺灣華語 (Taiwanese)
root@GL-XE300:~#

I can see that there are packages for your device in the repository

http://download.gl-inet.com/releases/packages-3.x/ath79/packages/
изображение

Yes it is there now.