I can confirm the problem. Thanks for reporting it.
Specifically:
Debugger entered--Lisp error: (wrong-type-argument listp (name . "Recentf"))
selectrum-helm--normalize-source((name . "Recentf") nil)
#f(compiled-function (source) #<bytecode 0x1f5e412531d40a>)((name . "Recentf"))
mapcar(#f(compiled-function (source) #<bytecode 0x1f5e412531d40a>) ((name . "Recentf") (init lambda nil (require ...) (when helm-turn-on-recentf ...)) (candidates lambda nil recentf-list) (keymap keymap (24 keymap ...) (67108925 . helm-ff-run-ediff-file) (3 keymap ... ... ... ... ... ... ... ... ...) (27 keymap ... ... ... ... ... ... ... ... ... ...) (19 . helm-ff-run-grep) (29 . helm-ff-run-toggle-basename) keymap (f13 lambda nil ... ...) (f12 lambda nil ... ...) (f11 lambda nil ... ...) (f10 lambda nil ... ...) (f9 lambda nil ... ...) (f8 lambda nil ... ...) (f7 lambda nil ... ...) (f6 lambda nil ... ...) (f5 lambda nil ... ...) (f4 lambda nil ... ...) (f3 lambda nil ... ...) (f2 lambda nil ... ...) (menu-bar keymap ...) (help keymap ...) (23 . #f(compiled-function () ... #<bytecode -0x1afdcdcb78da9c6d>)) (f1 lambda nil ... ...) (8 keymap ... ... ... ... ...) ...) (action ("Find file" . helm-find-many-files) ("Find file as root" . helm-find-file-as-root) ("Find file other window" . helm-find-files-other-window) ("Find file other frame" . find-file-other-frame) ("Open dired in file's direc..." . helm-open-dired) ("Attach file(s) to mail buf..." . helm-ff-mail-attach-files) ("Marked files in dired" . helm-marked-files-in-dired) ("Grep File(s) `C-u recurse'" . helm-find-files-grep) ("Zgrep File(s) `C-u Recurse..." . helm-ff-zgrep) ("Pdfgrep File(s)" . helm-ff-pdfgrep) ("Insert as org link" . helm-files-insert-as-org-link) ("Checksum File" . helm-ff-checksum) ("Ediff File" . helm-find-files-ediff-files) ("Ediff Merge File" . helm-find-files-ediff-merge-files) ("Etags `M-., C-u reload tag..." . helm-ff-etags-select) ("View file" . view-file) ("Insert file" . insert-file) ("Add marked files to file-c..." . helm-ff-cache-add-file) ("Delete file(s)" . helm-ff-delete-files) ("Copy file(s) `M-C, C-u to ..." . helm-find-files-copy) ("Rename file(s) `M-R, C-u t..." . helm-find-files-rename) ("Symlink files(s) `M-S, C-u..." . helm-find-files-symlink) ("Relsymlink file(s) `C-u to..." . helm-find-files-relsymlink) ("Hardlink file(s) `M-H, C-u..." . helm-find-files-hardlink) ("Open file externally (C-u ..." . helm-open-file-externally) ...) (persistent-action . helm-ff-kill-or-find-buffer-fname) (persistent-help . "Show this file") (help-message . helm-generic-file-help-message) (requires-pattern . 0) (candidate-transformer helm-skip-boring-files helm-w32-pathname-transformer) (filtered-candidate-transformer helm-highlight-files helm-fuzzy-highlight-matches) (action-transformer helm-transform-file-load-el helm-transform-file-browse-url helm-transform-file-cache) (pattern-transformer . helm-recentf-pattern-transformer) (match helm-mm-exact-match helm-mm-match helm-mm-3-migemo-match) (redisplay . identity) (mode-line "File(s)" "\\<helm-map>\\[helm-help]:He...") (header-line . "C-j: Show this file (keepi...") (multimatch) (match-part lambda (candidate) (if ... ... candidate)) (group . helm-files) (migemo)))
selectrum-helm--normalize-sources(helm-source-recentf)
selectrum-helm--adapter(:sources helm-source-recentf :ff-transformer-show-only-basename nil :buffer "*helm recentf*")
apply(selectrum-helm--adapter (:sources helm-source-recentf :ff-transformer-show-only-basename nil :buffer "*helm recentf*"))
helm(:sources helm-source-recentf :ff-transformer-show-only-basename nil :buffer "*helm recentf*")
helm-recentf()
funcall-interactively(helm-recentf)
call-interactively(helm-recentf record nil)
command-execute(helm-recentf record)
execute-extended-command(nil "helm-recentf" nil)
funcall-interactively(execute-extended-command nil "helm-recentf" nil)
call-interactively(execute-extended-command nil nil)
command-execute(execute-extended-command)
Is it something that can be done here or on helm side?
This is almost certainly not a Helm bug. It is just selectrum-helm.el not being quite good enough at emulating the Helm API. To fix the problem will require somebody to see what selectrum-helm.el is doing wrong (i.e. differently than Helm) when manipulating the sources list.
I'm seeing what looks like the same problem with helm-ag:
Debugger entered--Lisp error: (wrong-type-argument listp (name . "AG"))
selectrum-helm--normalize-source((name . "AG") nil)
#f(compiled-function (source) #<bytecode 0x1556ddf71476cc75>)((name . "AG"))
selectrum-helm--normalize-sources(helm-source-do-ag)
[snip]
gotta say, selectrum-helm-mode is super cool though. I don't think I would have tried this out yet if it weren't for that. I can try to find a fix at some point but likely won't have time in the next bit here.
@clemera Close this?
@Compro-Prasad See #466 selectrum-helm.el has been removed from Selectrum.