You're right: some people are reporting issues with the "Welcome" and "Software Boutique" not working in Ubuntu MATE 22.04 LTS ("Jammy Jellyfish"). I've found the following two related topics also here in the "Ubuntu MATE Community" Discourse discussion forums:
First topic / discussion started by user @randomdave about 4 months ago (on 26th April 2022):
Second topic / discussion started by user @mickee about 2 weeks ago (on 19th August 2022):
Two weeks ago (on 20th August 2022), I've participated in that second topic with what I found about this issue. Link to my post:
In that post of mine, I've pointed to the following Issue / Bug that was reported by @tmt (https://launchpad.net/~tallosho) on 21st June 2022:
You may want to click on the "This bug affects 6 people. Does this bug affect you? " link in that Launchpad bug web page (to add yourself to the list of affected users by that bug) and you may also want to add a comment in that page to report your experience about this bug.
For the record, I have upgraded a week ago from Ubuntu MATE 20.04.5 LTS ("Focal Fossa") to Ubuntu MATE 22.04.1 LTS ("Jammy Jellyfish") and the bug didn't happen / isn't happening to me, but it's obviously happening to you and other people.
