Spurious search plugin issues - "There aren't any seach plugins installed", can't install new plugins, plugin upgrade issue "plugin not supported"

[FranciscoPombal]

NOTE: A known workaround exists

This has been posted in various other issue reports and the forum:

• Close qBittorrent, delete the search engine files/settings (ref. https://github.com/qbittorrent/qBittorrent/wiki/Frequently-Asked-Questions#Where_does_qBittorrent_save_its_settings) and start qBittorrent again.

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This problem has been previously reported in several issue reports such as:

https://github.com/qbittorrent/qBittorrent/issues/11149 https://github.com/qbittorrent/qBittorrent/issues/11872 https://github.com/qbittorrent/qBittorrent/issues/9287 https://github.com/qbittorrent/qBittorrent/issues/11223

• Could be a nova/nova3 issue.
• Might be caused by a bad search plugin or bad plugin upgrade (?)
• Sometimes connected to the upgrade of qBittorrent versions (e.g. 4.1.x -> 4.2.x), but this is not consistent.
• The issue seems to be cross-platform - was at least observed on Linux and Windows.
• No reliable and precise steps to reproduce have been posted so far.
• Could be related to Python 2 (2)

I think there is enough "user story" information spread across those issues at this point. Now we need more advanced and precise information, e.g. from debugging the program.