UPDATE: It also closes by it self, and then opens, and like that all the time. I keep seeing this on the logs:

ene 07 08:03:57 artorias steamwebhelper[19790]: steamwebhelper.sh[19779]: Using supervisor /home/alosarjos/.steam/root/ubuntu12_32/steam-runtime/amd64/usr/bin/steam-runtime-supervisor
ene 07 08:03:57 artorias steamwebhelper[19790]: steamwebhelper.sh[19779]: Starting steamwebhelper under bootstrap sniper steam runtime via /home/alosarjos/.local/share/Steam/ubuntu12_64/steam-runtime-sniper.sh
ene 07 08:03:57 artorias steamwebhelper[19790]: steamwebhelper.sh[19779]: Using CEF sandbox \(try with -no-cef-sandbox if this fails\)
ene 07 08:03:57 artorias steamwebhelper[19790]: steamwebhelper.sh[19779]: Starting steamwebhelper with Sniper steam runtime at /home/alosarjos/.local/share/Steam/ubuntu12_64/steam-runtime-sniper/_v2-entry-point
ene 07 08:03:57 artorias steamwebhelper[19790]: exec ./steamwebhelper -nocrashdialog -lang=es_ES -cachedir=/home/alosarjos/.local/share/Steam/config/htmlcache -steampid=13066 -buildid=1736213535 -steamid=76561198402716199 -logdir=/home/alosarjos/.local/share/Steam/logs -uimode=7 -startcount=8 -steamuniverse=Public -realm=Global -clientui=/home/alosarjos/.local/share/Steam/clientui -steampath=/home/alosarjos/.local/share/Steam/ubuntu12_32/steam -launcher=0 -no-restart-on-ui-mode-change --valve-initial-threadpool-size=4 --valve-enable-site-isolation --enable-smooth-scrolling --password-store=basic --log-file=/home/alosarjos/.local/share/Steam/logs/cef_log.txt --disable-quick-menu --enable-features=PlatformHEVCDecoderSupport --disable-features=SpareRendererForSitePerProcess,DcheckIsFatal,ValveFFmpegAllowLowDelayHEVC
ene 07 08:07:00 artorias steamwebhelper[20179]: steamwebhelper.sh[20168]: Using supervisor /home/alosarjos/.steam/root/ubuntu12_32/steam-runtime/amd64/usr/bin/steam-runtime-supervisor
ene 07 08:07:00 artorias steamwebhelper[20179]: steamwebhelper.sh[20168]: Starting steamwebhelper under bootstrap sniper steam runtime via /home/alosarjos/.local/share/Steam/ubuntu12_64/steam-runtime-sniper.sh
ene 07 08:07:00 artorias steamwebhelper[20179]: steamwebhelper.sh[20168]: Using CEF sandbox \(try with -no-cef-sandbox if this fails\)
ene 07 08:07:00 artorias steamwebhelper[20179]: steamwebhelper.sh[20168]: Starting steamwebhelper with Sniper steam runtime at /home/alosarjos/.local/share/Steam/ubuntu12_64/steam-runtime-sniper/_v2-entry-point
ene 07 08:07:01 artorias steamwebhelper[20179]: exec ./steamwebhelper -nocrashdialog -lang=es_ES -cachedir=/home/alosarjos/.local/share/Steam/config/htmlcache -steampid=13066 -buildid=1736213535 -steamid=76561198402716199 -logdir=/home/alosarjos/.local/share/Steam/logs -uimode=7 -startcount=9 -steamuniverse=Public -realm=Global -clientui=/home/alosarjos/.local/share/Steam/clientui -steampath=/home/alosarjos/.local/share/Steam/ubuntu12_32/steam -launcher=0 -no-restart-on-ui-mode-change --valve-initial-threadpool-size=4 --valve-enable-site-isolation --enable-smooth-scrolling --password-store=basic --log-file=/home/alosarjos/.local/share/Steam/logs/cef_log.txt --disable-quick-menu --enable-features=PlatformHEVCDecoderSupport --disable-features=SpareRendererForSitePerProcess,DcheckIsFatal,ValveFFmpegAllowLowDelayHEVC

The same thing happens to me on Debian.

if you right click on the steam notification icon, and switch in bigPicture mode / normal mode... does this change anything ?

probably the same issue here :
https://github.com/ValveSoftware/steam-for-linux/issues/11558

now getting affected by this issue on stable release 1.0.0.81-2, arch linux as well

I getting this problem since couple of days ago, what was the fix?

in my case an update fixed it on archlinux

Deleting index.theme in ~/.icons/default/ fixed it for me.

https://github.com/ValveSoftware/steam-for-linux/issues/11873#issuecomment-2776220403

I'm not getting this behavior anymore